REPORTS AND STUDIES

75

ESTIMATES OF OIL ENTERING 

THE MARINE ENVIRONMENT 

FROM SEA-BASED ACTIVITIES
75REPORTS AND STUDIES

IMO FAO UNESCO-IOC WMO UNIDO IAEA UN UNEP

ESTIMATES OF OIL ENTERING

THE MARINE ENVIRONMENT

FROM SEA-BASED ACTIVITIES

INTERNATIONAL MARITIME ORGANIZATION

London, 2007
Notes

1. GESAMP is an advisory body consisting of specialized experts nominated by the Sponsoring Agencies (IMO,

FAO, UNESCO-IOC, UNIDO, WMO, IAEA, UN, UNEP). Its principal task is to provide scientific advice concerning

the prevention, reduction and control of the degradation of the marine environment to the Sponsoring Agencies.

2. This study is available in English only from any of the Sponsoring Agencies.

3. The report contains views expressed or endorsed by members of GESAMP who act in their individual capacities; their views may not necessarily correspond with those of the Sponsoring Agencies.

4. Permission may be granted by any of the Sponsoring Agencies for the report to be wholly or partially reproduced in publication by any individual who is not a staff member of a Sponsoring Agency of GESAMP, provided

that the source of the extract and the condition mentioned in 3 above are indicated.

ISSN 1020-4873

ISBN 978-92-801-4236-5

© UN, UNEP, FAO, UNESCO-IOC, WMO, UNIDO, IMO, IAEA 2007 

For bibliographic purposes this document should be cited as:

GESAMP (IMO/FAO/UNESCO-IOC/UNIDO/WMO/IAEA/UN/UNEP Joint Group of Experts on the Scientific Aspects

of Marine Environmental Protection). 2007. Estimates of oil entering the marine environment from sea-based activities. Rep. Stud. GESAMP No. 75, 96 pp.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · i

Table of Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Members of the Oil Input Working Group (GESAMP WG 32) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

EXECUTIVE SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Scope of task . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Overview of the report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2 METHODS - MAKING ESTIMATES OF OIL ENTERING THE

SEA FROM SHIPS AND OTHER SEA-BASED ACTIVITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 The general approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.2 Limitations and uncertainties of methodology – inputs from ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.1 Operational discharges – cargo-related. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.2.2 Operational discharges – ship-related (bilge oil and fuel oil sludge) . . . . . . . . . . . . . . . . . . . . . 5

2.2.3 Air pollution from ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3 Accidental spillage methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3.1 International Oil Spill Database (IOSD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.3.2 Estimation factor for smaller spills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.3 Application of the small spill estimation factors to the IOSD . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3.4 Average annual input estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

2.3.5 Definition of accidental spillage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3.6 Regional analysis of accidental spillage data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.4 Produced water discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.5 Operational discharges from coastal refineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 OIL INPUTS FROM SHIPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 Operational discharges – ship-related . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1.2 Operational engine room wastes and discharges (fuel oil sludge and bilge oil) . . . . . . . . . . . . 13

3.1.3 Oily ballast from fuel tanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1.4 Total operational discharges – ship-related: Total amount of oil discharged from

engine rooms (all ships) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.1.5 Air emissions - VOCs from tankers – “Volatile Organic Compounds” . . . . . . . . . . . . . . . . . . . 15

3.1.6 VOCs from onboard bunkering and engine operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.2 Operational discharges – cargo-related . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.2 Tanker construction and legislation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.2.3 Tanker fleet size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.4 Assumptions to the outflow model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.4.1 Crude oil tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.2.4.2 Product and chemical tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2.5 Distinction between short haul and long haul voyages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

3.2.6 Voyage frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2.7 Summary of operational discharges – cargo-related . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

3.3 Accidental discharges of oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.1 Accidental spillage from all sea-based activity sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3.3.2 Accidental discharges from ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.2.1 Accidental discharges from tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.2.2 Accidental discharges from non-tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3.3.3 Accidental spillage in relation to sea-borne oil trade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

3.3.4 Regional analysis of accidental spillage data from all sources . . . . . . . . . . . . . . . . . . . . . . . . 32

3.3.5 Sunken vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3.5.1 Merchant vessel casualties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

3.3.5.2 Military vessel casualties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
ii · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

3.4 Dry docking of ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.4.1 Tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.4.2 Other vessels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.5 Recycling of ships . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.5.1 Hydraulic oils, lubricating oils and fuels (all ships) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.2.5 Cargo residues/ oil sludge (tankers) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

3.6 Operational discharges from ships operating under sovereign immunity . . . . . . . . . . . . . . . . . . . . . . 42

3.7 Deliberate discharges of oil to save life at sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4 EXPLORATION AND PRODUCTION IN THE OFFSHORE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2 Operational discharges from offshore installations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2.1 Machinery space discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

4.2.2 Drilling discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.2.3 Produced water discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

4.2.4 Air emissions (Non-methane volatile organic compounds or VOCs) . . . . . . . . . . . . . . . . . . . . 46

4.3 Accidental discharges from exploration and production activities . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

4.4 Pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.4.1 Operational discharges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.4.2 Accidental releases from pipelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

4.5 Offshore exploration and production - Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5 OTHER INPUTS OF OIL INTO THE SEA FROM SEA-BASED

ACTIVITIES AND RELATED TOPICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.1 Coastal refineries, oil storage facilities and marine terminals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.1.1 Operational oil inputs from coastal refineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.1.2 Accidental releases from coastal facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.2 Reception facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.3 Oil in waste materials dumped at sea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.4 Fuel dumps from aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.5 Small craft activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.5.1 Outboard engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

5.5.2 Inboard engines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5.5.3 Small craft activity: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.6 Natural oil seeps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

5.7 Rocket launches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.8 Tar distributions and their significance regarding inputs from ships . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.9 Oil inputs from unidentified point sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6 SUMMARY AND CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

6.2 Data and information needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

7 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64

8 BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

ANNEX – Glossary and Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · iii

Spilled oil from sea-based activities continues

to be a marine pollutant in coastal and offshore

waters. This is despite many successful regulatory

initiatives at international and national levels, and

the considerable efforts that are being made by the

oil and shipping industries to reduce the number

of accidents and to reuse, recycle and filter oily

wastes aboard ships. This study develops a

methodology and presents updated estimates of

global inputs of oil, as defined under the MARPOL

73/78 Convention, that originate from shipping and

other sea-based activites.

The report addresses the methods that can be

used for making such estimates of input and the difficulties and uncertainties involved. Ship-based

activities are the primary focus. These activities

include ships, offshore oil and gas exploration and

production, and the onshore facilities related to both

operations, including refineries and all associated

infrastructures. Estimation of operational ship

inputs, both cargo and ship related, was a primary

focal point of this study and required knowledge of

vessel types and structures, operations, the oil trade,

and MARPOL 73/78 regulations. Data on other

inputs were obtained from many sources, published

and unpublished. Considerable effort has been made

to assemble data and conduct trend analysis of accidental spills from ships and other sea-based activities, from the late 1960s onwards.

Some other important input topics are briefly

presented. These include volatile organic compounds (VOC) emissions from shipping, inputs from

sunken vessels (casualties), inputs from recreational

boating, and oil seeps. These help to supplement the

picture of inputs from sea-based activities. Inputs

from VOC emissions and recreational boating may be

very substantial, but methods for making global estimates are very uncertain. Pelagic and littoral tar is

discussed as tar is found on beaches worldwide and

can be a monitor of shipping discharges.

The Working Group strived to identify all sources

of oil from ships and sea-based activities, to reach

reasonable estimates of current annual inputs to the

oceans from these sources, and to point out areas of

uncertainty. The input values are estimates, from

both calculations and measurements. With the

exception of data on accidental discharges, most

estimates lack ranges or confidence limits, i.e.

measures of variability. The greatest value of the

presented input numbers, therefore, is that they give

a picture of relative inputs from the different global

ship and sea-based sources and they point to input

sources requiring additional research, monitoring,

assessment, regulatory and industry attention. The

study presents recommendations for improving our

ability to provide oil input estimates, a knowledge of

which will ultimately contribute to global marine environmental protection related to sea-based activities.

This study was conducted by the GESAMP Oil

Inputs Working Group, the members of which are

listed below. The Group is very grateful to the many

persons providing data and information for this

study. Funding for this work came from IMO. Other

agencies (IAITO, ITOPF, Environment Canada, and

E&P Forum) supported some of the working group

members. The Cutter Information Corp., USA, provided one of the primary data bases, but disclaims

all warranties as to the accuracy, completeness or

adequacy of the information provided to IMO, and

has no liability for damages resulting in the use of

this data. GESAMP members reviewed the report on

several occasions from 1999-2003; they are thanked

for these special efforts. The report was technically

reviewed by J. N. Butler (USA), M. Fingas (Canada),

T. Gunner (Norway), S. Hara (Japan), K. Kvenvolden

(USA), R. Law (UK), J. Payne (Canada), J. Phinney

(USA), R. Pond (USA), J. A. Sanchez Cabeza (Spain),

K. Skjolsvik (Norway), D. Walker (USA), and F. Wiese

(Canada), whom the Group thanks immensely for

their special efforts

The Working Group received considerable support from Dr. Manfred Nauke, IMO (retired), and Mr.

René Coenen, Marine Environment Division, IMO,

who in their capacity as technical secretaries of

GESAMP graciously and efficiently assisted the

study. At IMO, Ms. Jennie Hallett assisted the working group at its early meetings, and Ms. Jennifer

Francis greatly assisted with the co-ordination of the

technical reviews and preparation of the final manuscript. The report was revised and edited through

several drafts by Dr. P. G. Wells, Chair of the Working

Group, who accepts responsibility for any errors or

omissions that remain. The Group and IMO solicit

comments from the reader on any aspect of this

topic. 

“There must be a beginning of any great matter,

but the continuing unto the end until it be thoroughly finished yields the great glory.” 

Sir Francis Drake

Dedication

This report is dedicated to Dr. Manfred Nauke,

recently retired from the Marine Environment

Division, IMO, and the GESAMP Secretariat. Dr.

Nauke provided leadership, inspiration, knowledge

and support for many GESAMP working groups and

their members over many years, and was instrumental at initiating the Oil Inputs Working Group. He

symbolizes the excellence of individual marine professionals who, through extraordinary commitment

and efforts throughout their careers, contribute substantially to the protection and conservation of the

global seas and their living resources for present and

future generations.

Preface Acknowledgments
iv · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Dr. Peter G. Wells (Chairman)

Ecosystem Science and Information Division

Canadian Wildlife Service 

Environmental Conservation Branch

Environment Canada

45 Alderney Drive

Dartmouth, Nova Scotia

Canada B2Y 2N6

Tel: +1 902 426 1426

Fax: +1 902 426 6434

Email: peter.wells@ec.gc.ca

Mr. John Campbell

Technical Director, International Association of

Oil and Gas Producers

25-28 Old Burlington Street

London W1X 1LB

United Kingdom

Tel: +44 (0)20 7292 0603

Fax: +44 (0)20 7434 3721

Email: john.campbell@ogp.org.uk

Ms. Dagmar Schmidt Etkin

Environmental Research Consulting

41 Croft Lane, Cortlandt Manor

NY10567-1160

USA

Tel: +1 914 734 7511

Fax: +1 914 734 2256

Email: etkin@environmental-research.com

Dr. John S. Gray1

Biology Institute, University of Oslo

P.B. 1064, N-0316 Blindern

Norway

Tel: +47 228 54510

Fax: +47 228 54438

Email: j.s.gray@bio.uio.no

Ms. Catherine Grey2

The International Tanker Owners Pollution

Federation Limited (ITOPF)

Staple Hall, Stonehouse Court

89-90 Houndsditch

London EC3A 7AX

United Kingdom

Tel: +44 (0)207 621 1255

Fax: +44 (0)207 621 1783

Email: central@itopf.com

Dr. Paul Johnston

Greenpeace Research Laboratories

Department of Biological Sciences

University of Exeter

Prince of Wales Road

Exeter EX4 4PS

United Kingdom

Tel: +44 (0)1392 413019

Fax: +44 (0)1392 423635

Email: p.Johnston@exeter.ac.uk

Mr. Jens Koefoed

Bdoey Ale 11

0257 Oslo 2

Norway

Tel: +47 22 454500

Fax: +47 22 454780

Email: koefoed@sjofartsdir.dep.no

Mr. T.A. Meyer3

The International Association of Independent

Tanker Owners

Baltic Exchange

38 St. Mary Axe

London EC3A 8BH

United Kingdom

Tel: +44 (0)207 623 4311

Fax: +44 (0)207 626 7078

Email: Trygve@grobu26.demon.co.uk

Mr. Fionn C. Molloy4

The International Tanker Owners Pollution

Federation Limited (ITOPF)

Staple Hall, Stonehouse Court

87-90 Houndsditch

London EC3A 7AX

United Kingdom

Tel: +44 (0)207 621 1255

Fax: +44 (0)207 621 1783

Email: fionnmolloy@itopf.com

Mr. Tim Wilkins5

The International Association of Independent

Tanker Owners

St. Clare House

30-33 Minories

London EC3N 1DD

United Kingdom

Tel: +44 (0)207 977 7016

Fax: +44 (0)207 977 7011

Email: tim.wilkins@intertanko.com

IMO Technical Secretaries of GESAMP

Dr. Manfred Nauke

(sessions 1 to 4 of Working Group)

Mr. René Coenen

(sessions 5 and 6 of Working Group)

Marine Environment Division

International Maritime Organization

4 Albert Embankment

London SE1 7SR

United Kingdom

Tel: +44 (0)207 587 3239

Fax: +44 (0)207 587 3210

Email: rcoenen@imo.org

Members of the Oil Input Working Group (GESAMP WG 32)

1 Attended Working Group Meeting 3 only.

2 Attended Working Group Meetings 1 and 2 only.

3 Attended Working Group Meetings 1 to 3.

4 Participated in Working Group Meetings 4, 5 and 6.

5 Participated In Working Group Meetings 4, 5 and 6.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · v

1 Introduction

ES-1 As part of the global effort to reduce oil

inputs into the marine environment from ships and

other sea-based activities, an independent detailed

assessment of inputs from the various sources is

periodically required. This has been conducted previously (GESAMP 1976, 1993; MEPC 1990; The

National Research Council of USA, NRC 1975, 1985,

2003; amongst others). In the late 1990s, the Marine

Environment Protection Committee (MEPC) of IMO

requested GESAMP to evaluate carefully all available

data sources on oil inputs into the marine environment from sea-based activities (i.e. maritime transportation, offshore exploration and production), and

particularly to develop approaches that might be

used for the provision of such input data. Hence, the

terms of reference of the GESAMP Oil Input Working

Group were to estimate current annual amounts of oil

entering the marine environment from sea-based

activities, and to focus particularly on improving the

methodology of making such estimates. This report

addresses both inputs and methodologies for making estimates, and places the various types of oil

source inputs from ships and ship-related activities

into perspective. The report covers four areas:

approaches to making estimates of oil inputs, oil

inputs from ships, oil inputs from offshore exploration and production, and other oil inputs and related topics.

2 Approaches to making estimates of

oil inputs into the sea

ES-2 Obtaining reliable and up-to-date data

on quantities of oil entering the marine environment

from all of the different ship and other sea-based

sources is not a simple task. Some inputs have to be

calculated (i.e. operational inputs from ships). Few

countries have reliable databases, thus this report

relies heavily on spill and other input data available

for the North Sea and for North American waters.

Data on inputs are lacking or are inaccessible from

key areas such as the Middle East, South America

(e.g. Brazil), West Africa and South-East Asia. It is

important that steps be taken to ensure that data on

oil entering the marine environment in all of these

geographic areas are routinely obtained, stored and

transmitted to international databases. Further

problems relating to operational oil input data relate

to the fact that changes are taking place continually

in shipping fleets, such as ship design and tonnage,

and in volumes of crude oil transported. Newer

ships are cleaner, and represent a growing percentage of various fleets. Volumes of oil originating from

different countries are not constant. Such changes

have to be taken into account when calculating

inputs of oil to the sea from ship operations.

ES-3 The methodology was extensively

revised and re-modelled to estimate operational

inputs from ships, owing to extensive legislation and

the specialization with regard to vessel type, function, performance and regulatory requirements.

Hence, different methodologies from both the original 1990 Report (MEPC 1990) and between the various sources of oil discharge from ships have been

used in the current report. Inputs of bilge oil and fuel

oil sludge are the most extensively evaluated

sources.

ES-4 Much of the data used in the analysis of

spillage from all point sources, including vessels,

pipelines, facilities, and offshore exploration and

production activities, were derived from records in

the International Oil Spill Database (IOSD) of Cutter

Information Corp., and records in the databases of

Environmental Research Consulting (ERC), USA.

Each of the databases has extensive information on

individual spill incidents. This includes information

on spill date, location, source type, source name,

and the amount and type of oil spilled. Data on spill

incidents in the IOSD and ERC databases, as well as

other compiled data on which these databases rely,

are collected from a large number of reputable

sources on an international basis e.g. the ITOPF

Tanker spills database and personal contacts. Due

to the nature of the data collection process, discrepancies and inaccuracies exist in these databases

and original data sources. Since the IOSD contains

no verified information on oil spills below 34 tonnes

and the ERC databases contain incomplete information on oil spills in this smaller range, a “small spill

estimation factor” was calculated for both the number of spills and the amount of oil spilled in incidents

involving less than 34 tonnes.

ES-5 Estimates for oil inputs from produced

water at offshore wells and from refineries near-shore

were based on extrapolations from best available

data and assumptions on compliance with existing

regulations and guidelines.

ES-6 Sources of data and information on oil

discharges from ships and boats are extensive in the

published literature, but uneven in detail and quality.

They were used where appropriate and reliable. An

extensive source bibliography was compiled during

the study.

3 Oil inputs from ships

ES-7 Operational oil discharges from ships

were estimated. Operational discharges of oil into

the marine environment from ships depend on several factors. These include: type and age of ship; level

of maintenance of ship and engines; presence of oilwater separators and other equipment designed to

curtail discharges of oil; practice of the LOT (loadon-top) principle; training and vigilance of the crew;

level of shipping activity; and presence of adequate

reception facilities. To estimate the fuel sludge discharge figures for all ships including tankers, it was

EXECUTIVE SUMMARY
vi · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

necessary to estimate at the outset the bunker consumption for all ships, tankers and other ships. The

bunker consumption per vessel was estimated, followed by estimates of sludge generation and compliance with the MARPOL discharge allowance of

15ppm. In summary, total operational discharges

into the marine environment of bilge oil and fuel oil

sludge from all ships are approximately ~188,000

tonnes/yr. Oily ballast (fuel tanks) discharges into

the sea from ship operations was estimated to be

~900 tonnes/yr.

ES-8 Operational discharges associated with

tanker cargoes, i.e. tank washing and oil in ballast

water, were estimated. Due to the lack of complete

data for movements of tankers, and owing to the

potential for one cargo to be carried by a number of

vessels, the numbers of tankers were used as the

basis of the estimates of oil transportation and subsequent cargo- related operational discharges.

Tanker construction, fleet size, and assumptions to

an outflow model (taking into account tanker type,

voyage length and frequency) were considered for

the new estimates of oil inputs. The methodology

and calculations are complex, but the approach is

original and believed to give the best input estimates. The estimated discharge of oil into the

marine environment from cargo-related tanker activities, which includes tank washing and oil in ballast,

is 19,250 tonnes/yr., or ~ 19,000 tonnes/yr. 

ES-9 Oil cargoes release VOCs during loading

operations and transport, and the operation of ships

results in the release of VOCs from the engines and

funnels. VOCs go into the atmosphere and a fraction

returns to the sea surface. The total discharge into

the atmosphere of VOCs from the carriage at sea of

crude oil by tankers would be 3,085,072 tonnes/yr.,

or ~3,000,000 tonnes/yr. VOCs from loading must

also be added to this figure. Hence, the total emission of VOCs from tanker operations is: 3,085,075

tonnes (Carriage) + 3,712,961 tonnes (Loading) =

6,798,036 tonnes, or ~6,800,000 tonnes/yr. To

establish the volume of this emission that enters the

sea, it was necessary to establish which fractions

within the VOCs would precipitate. Pentane contributes approximately 1% of VOC. As this is the

main component with a boiling point above 0 deg. C

(36 deg. C), this is the main fraction of VOCs that

could enter the sea due to its solubility. Hence,

67,980 tonnes/yr. or ~68,000 tonnes/yr. of “oil” constituents from VOC emissions may enter the

oceans.

ES-10 Accidental oil discharges from ships and

other sea-based activities are thoroughly evaluated.

The IOSD is described, especially in regard to units

and conversions, data reporting and collection, and

the definition of “accidental spillage”. A statisticallyderived correction factor for spills smaller than 34

tonnes was generated and used throughout this

evaluation in order to correct for the absence of

small spills, those between 0.17 and 34 tonnes, in

both spill number and spill amount estimates.

Looking first at accidental spillage from all sources,

after rising in the first decade between 1968 and

1977, spill numbers have dropped and levelled off in

the last 15 years. Over the three 10-year periods

evaluated in this study (1968-1997), spill amounts

have dropped but there are unusual peaks in 1979

(associated with the Ixtoc I well blowout in the Gulf

of Mexico, and 3 large tanker spills), 1983 and 1991.

Vessels consistently constituted the largest source of

accidental spillage over all time periods. The best

estimates of annual oil inputs into the marine environment from accidental releases from all sources

during the 3rd 10 year period, 1988-1997, are: vessels

– 163,200 tonnes; coastal facilities – 2,400 tonnes;

pipelines – 2,800 tonnes; exploration and production

- 600 tonnes; other/unknown sources - 200 tonnes;

and war related activities – 1,052,300 tonnes. The

total input from accidental sea-based releases (without the war-related annual input) is ~169,000

tonnes/yr.

ES-11 The annual percentage of spills from all

sources involving 5,000 tonnes or more has

declined considerably since 1968, but it has

remained steady at about 0.2 % of spills for the last

10 year period (1988-97), or 4.1 spills of this size

annually on average, most of which (93%) involve

vessels. Catastrophic exploration and production

activity spills are much less frequent than large

tanker spills e.g. Ixtoc I was a rare event. If one

eliminates from consideration the spills over 5000

tonnes and the unique 1991 Gulf War spillages,

the contributions from vessels and coastal facilities

drop, resulting in a total accidental release input

of 68,700 tonnes/yr. Smaller spills, particularly

those under 34 tonnes (i.e. 10,000 US gal., an

arbitrary division), make up nearly 97% of the number of annual spills, although together they contribute less than 16% of the amount of oil entering

the sea annually from accidents. In general, over the

last ten-year period evaluated (1988-97), the occurrence of accidental spills of all sizes has declined

in most global regions compared to the previous

two 10-year periods (exceptions being the Black

Sea, portions of Africa, the Persian Gulf and

Australia). 

ES-12 Considering accidental discharges from

ships alone, the number of spills over 0.17 tonnes

(50 US gal. – a regulated volume in the USA) and

amounts spilled both rose during the 1960s to a peak

in 1979, then dropped and levelled off by the mid1980s to a mean annual spillage of 163,200 tonnes

from vessels during 1988-97. The amount of oil

spilled annually from tankers has declined steadily

since the late 1960s, to 157,900 tonnes per year

from 1988-97. Spills from non-oil cargo vessels have

increased significantly in number over the past 30

years (1968-97) – 53 spills, 740 spills and 1049 spills

per year on average for the three 10-year periods

that were considered. Correcting the data for small

spills, the best estimate of oil inputs into the sea

from accidental releases from vessels of all types

(e.g. tankers, barges, non-oil cargo) during the years

1988-1997 is 163,200 tonnes annually (range of

46,000-256,000 tonnes). 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · vii

ES-13 Analyses were conducted of accidental

spillage in relation to oil production and tanker transport over the past 30 years (1968-1997) in order to

correct the spill statistics for increases in oil production and transport. The mean annual number of

spills (of at least 0.17 tonnes) rose from 0.60 spills

per million tonnes produced in 1968-77, to a peak of

1.39 spills per million tonnes produced in 1978-87,

then fell to 1.08 spills per million tonnes produced in

1988-97. The mean annual number of vessel spills

per million tonnes transported followed a similar pattern - 1.54 (1968-77), 2.57 (1978-87) and 2.02 (1988-

97). As well, the general trend is that the mean annual percentage of transported oil that is spilled has

decreased over the last 30 years. Despite greater

opportunities to spill more oil during the last period

evaluated, fewer tanker spills have occurred and less

oil has been spilled accidentally into the sea, compared with the previous two periods.

ES-14 The regional analysis of accidental

spillage data, using 18 regions to cover the globe,

shows that the large majority of spills, particularly

from vessels, still occur in port areas or in vessel

traffic lanes. All but 3 regions (Eastern Africa/Indian

Ocean, Persian Gulf, Australia and New Zealand)

showed decreases in the average annual amount

spilled in accidental releases over the past 30 years

(1968-97). The exceptional regions show either

increases due to more shipping traffic and wars (East

Africa, Persian Gulf) or no change in amount spilled

(Australia and New Zealand).

ES-15 Statistics were also gathered for sunken

vessels, both merchant and military. Between 1939

and 1997, a total of 21,486 vessels, i.e. ~21,500 vessels, were recorded as total losses. Many of these

have been lost together with their remaining bunker,

lubricating and hydraulic oils, and oil as cargo.

Losses in the smaller gross tonnage ranges are probably underestimated, yet these vessels may contain

significant quantities of oil. During this period, technology has improved for recovery of oil from casualties, and fuel types have changed to the modern

bunker oils. It is not yet possible to derive accurate

estimates for oil lost at sea globally by marine casualties and annual inputs from these sources. It is

well known, however, that such inputs are occurring

and may be significant in size and impact, especially at island states of the Western Pacific. Every effort

should continue to map ship locations, describe the

ships condition and the volumes of contained oil,

estimate the risks of and from release, and organize

an international effort to recover oil from casualties

of highest risk. 

ES-16 Oil enters the sea from dry-docked vessels. For tankers, based on the current fleet of 321.1

million dead-weight tonnes or DWT (circa 2000), the

annual discharge of oil from tankers in dry docks is

estimated to be 2569 tonnes. For other vessels such

as drybulkers, the estimate of annual discharge due

to dry-docking is 347 tonnes of oil, hence the total oil

discharge during dry-docking is estimated at 2916

tonnes/yr. or ~2900 tonnes/yr. 

ES-17 During recycling (previously called

scrapping) of ships, most frequently occurring on

beaches in countries of south-east Asia, oil can be

released if the ships were not made "gas-free" and

"slop-free" prior to demolition, or if the oil was

released during the tank cleaning operations en

route to the break-up locations. Two categories of

oil can be established to calculate the quantities of

oil discharged into the ocean during recycling operations: (1) fuels, hydraulic oils and lubricating oils (all

ships); and (2) cargo residues and oil sludge

(tankers). Estimates of oil inputs are 330 tonnes/yr.

and 14,500 tonnes/yr., respectively, for a total of

14,830 tonnes/yr. from recycling of ships. A massive

recycling of tankers is being anticipated during the

period 2003-2007. INTERTANKO predicts that 25

tankers will be phased out in 2003, 97 in 2004, 142

in 2005, 134 in 2006 and 71 in 2007, a total of 469

tankers over this five-year period, and making this

input source even more important for evaluation in

future studies.

4 Oil inputs from exploration and

production in the offshore

ES-18 Operational discharges of hydrocarbons

occur from the 6000 oil and gas installations currently working in the marine environment, the greatest

number (>4000) being in the Gulf of Mexico.

Operational discharges of oil or oily water from offshore installations are numerous. There are machinery space discharges; no estimates are available but

these are thought to be small. Drilling discharges

contribute due to the use of oil-based drilling muds;

these are now being phased out, but amounts

ranged between 3,180-14,248 tonnes oil per year on

cuttings for the North Sea, 1989-96. Produced water

also contributes, with annual oil input from produced

water for the Gulf of Mexico of 2900 tonnes, assuming 40 mg/l water; annual inputs for the North Sea

range between 4119 to 8109 tonnes oil, 1989-97,

with predictions of 12,000 tonnes by the year 2002.

Finally, there are air emissions or VOCs. Using the

average figures from the Gulf of Mexico (2900

tonnes/yr.), Australia (1450 tonnes/yr.), and the North

Sea (12000 tonnes/yr.), the total estimated annual

input of oil from offshore operations is estimated to

be 16,350 tonnes/yr. This is a minimum value as

data were not available for a number of active oil

fields.

ES-19 Accidental discharges of oil from exploration and production activities include spills from

platforms, wells and rigs but not pipelines, and are

expressed as numbers of spills and amounts spilled.

The largest spillages to date occurred in 1979 (Ixtoc

I, Gulf of Mexico) and 1983 (Nowruz, Iran). While

there have been no marine production and exploration spills over 2000 tonnes over the last decade,

there have been 7 spills over 350 tonnes, all but one

in the North Sea. The best estimate of oil input from

accidental releases during 1988-97 is 600 tonnes/yr.

While the probability of a catastrophic blow-out such

as Ixtoc has been vastly reduced by current method-
viii · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

ologies and technology, the possibility of such an

event always exists.

ES-20 Accidental releases from offshore or

coastal pipelines occur. Numbers of spills over 0.17

tonnes have risen sharply, from an average of 47 per

year (range 31-125) in 1968-77, to 188 (range 63-

438) in 1978-87, to 228 (range 125-438) in 1988-97.

This apparent upward trend may be due in part to

increased reporting of moderate-sized spills. Large

spills over 5,000 tonnes are rare events, being only

4.9% of all of the spills from this source. The best

estimate of oil input from offshore or coastal

pipelines during the years 1988-97 is 2,800

tonnes/yr. This spillage represents a slight increase

in amount spilled from this source compared to the

previous two periods.

5 Other oil inputs into the sea and

related topics

ES-21 There are both operational oil inputs and

accidental spillage from coastal facilities, i.e.

coastal refineries. In the most developed nations,

the effluents contain on average 5 ppm of oil, while

for developing nations and nations with refineries

that are not well maintained or operated, effluents

may contain an average of 25 ppm oil. Estimates are

based on the total crude refining capacities of

coastal or estuarine refineries, and their operating

conditions; hence the maximum total operational

input of oil from refineries would be approximately

180,000 tonnes of oil per year (worst case) or

45,000-180,000 tonnes of oil per year if the less efficient refineries were discharging at less than 25 ppm

or operating for shorter periods. A median value for

oil inputs from refineries is 112,500 tonnes/yr.

ES-22 Accidental releases from coastal facilities also occur. Numbers of spills decreased during

the 1988-97 period, while spill amounts stayed fairly

constant over 30 years except for 3 years (1978,

1981, and 1991). Smaller spills (i.e. those under 34

tonnes) make up more than 97% of the annual number of accidental spills from coastal refineries and

facilities. The best estimate of oil input from accidental releases from coastal facilities, including

refineries, marine terminals and storage facilities

during the years 1988-1997, is 2,400 tonnes/yr. 

ES-23 Inputs from coastal oil reception facilities may be significant, based on qualitative information on what they receive and how they function.

Inputs could not be estimated due to the unavailability of quantitative data.

ES-24 Inputs of oils in dredged materials are

probably insignificant; this source is well known as it

is regulated under the London Convention and

Protocol but global data were unavailable to the

Working Group. 

ES-25 Inputs of oils from small, predominantly

leisure craft were estimated, using mainly North

American data and a methodology reported by NRC

(2003). At 53,000 tonnes/yr., likely a very conservative value and much less than the GESAMP working

group originally estimated, small craft are a significant source of oil and its components into coastal

waters. The estimates require verification from

field measurements, better data on numbers and

types of recreational boats and engines in use worldwide, and consideration of future trends in engine

efficiency.

ES-26 Other topics included aircraft fuel

dumps, beach tar, and natural seeps, but were not

dealt with comprehensively. There are oil inputs from

fuel dumps from aircraft, rocket launches and

unknown point sources. Although not sea-based

activities directly, these occur over or near the sea.

As well, the significance of tar amounts and distributions on beaches as a reflection of oil discharges

from tankers and the efficacy of regulations under

MARPOL 73/78 is discussed. Likewise, natural

seeps are discussed briefly; at 600,000 tonnes/yr.,

conservatively, this is a natural but important source

of crude oil to the sea. 

6 Summary

ES-27 This study shows the wide range of

types and quantities of oil inputs from ship and other

sea-based activities, as well as the spatial and temporal variability of accidental spills globally. The

reader should view the input figures in a relative

sense, carefully noting the estimation methods

employed and their limitations. The most recent published information was also used where appropriate.

ES-28 The estimated average annual inputs of

oil entering the marine environment, in metric tonnes

per year (tonnes/yr.), from ships and other sea-based

activities, based on the most recent 10 year period of

data available (1988-97), are:

Totals:

- Ships 457,000

- Offshore exploration and production 20,000

- Ships plus offshore 477,000

- Coastal facilities 115,000

- Ships plus offshore plus coastal facilities 592,000

- Small craft activity 53,000

- Natural seeps 600,000

- Unknown (unidentified) sources 200

- GRAND TOTAL 1,245,200 tonnes/yr.

ES-29 Operational discharges from ships make

up 45% of the input of 457,000 tonnes/yr. (ships),

followed by shipping accidents at 36% of the input.

Fuel oil sludge from vessels is the major routine

operational input (~186,000 tonnes/yr.), or 68% of

ship operational inputs. There are important ecological reasons to try to reduce this input, especially in

coastal waters and in particularly sensitive marine

areas of international importance for the conservation of wildlife. 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · ix

ES-30 Oil tankers, which are often identified as

being major routine polluters, account for 4.2%

(~4%) of ship inputs as oil in ballast waters, an operational input. However, tanker and barge accidents

are a major input (158,000 tonnes/yr.), even with the

decline in large spills from tankers in recent years.

Accidents are a very variable input source, and bad

years, i.e. a large spill such as the Amoco Cadiz or

Exxon Valdez, can skew the statistics. Most accidents are coastal and many are damaging to marine

ecosystems, sometimes for years, regardless of spill

size. 

ES-31 Coastal facilities contribute significantly

to oil inputs, at 115,000 tonnes/yr. This is 25.2 % of

the ship input, or 19.4 % of the total of input from

ships, offshore and coastal facilities, combined.

VOC emissions from tankers, conservatively estimated at 68,000 tonnes/yr., make up 14.9% of total ship

inputs.

ES-32 The offshore oil inputs, often considered

by the public as a major input, represent a minimum

of 4.1% of the total input from both ships and the

offshore exploration and production (EandP) combined, or 4.3% of ship inputs. More data is required

to verify this estimated input as global data are limited.

ES-33 Small craft activity inputs are a serious

concern, based on amount and location. They represent a significant input of oil-derived hydrocarbons, albeit with estimates based largely on North

American data. Whether or not such inputs should

be included in this study on sea-based activities is

debatable, and the method used here to estimate

global inputs from small craft is preliminary. They

obviously, however, represent a large and chronic

input source of hydrocarbons to the coastal marine

environment, and deserve additional study.

ES-34 The study concludes with a series of recommendations for improving the oil input estimates

from sea-based activities. Such estimates are

important for assessing the efficacy of MARPOL

73/78 and relevant national legislation, and for estimating risks of oiling to coastal and offshore marine

ecosystems and living resources, in the years

ahead.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 1

1 Oil was the first of the recognized “marine

pollutants” to be controlled and regulated. This started with the International Convention for the

Prevention of Pollution of the Sea by Oil, 1954, and

many other specific international conventions,

including The International Convention for the

Prevention of Pollution from Ships, 1973, as modified

by the Protocol of 1978 relating thereto (MARPOL

73/78) (GESAMP 1993; IMO 2002; Carlin 2002).

National legislation has also been improved, as in the

United Kingdom following the Torrey Canyon spill of

1967, and in the United States following the Exxon

Valdez spill of 1989. As a result of cooperation

between governments, industry and intergovernmental organizations, many positive changes have taken

place in the oil and shipping industries to reduce oil

inputs from routine operations, and to recover oil

from small spills and large accidents.

2 However, oil continues to enter the world’s

oceans from shipping and ship-based activities,

through accidental spills and intentional discharges,

as well as from many land-based sources and natural oil seeps. In coastal areas, such inputs often

cause ecological damage and harm to public amenities (NRC, 1975, 1985, 2003; Boesch and Rabalais

1987; GESAMP 1977, 1993; Wells et al. 1995;

amongst others). The ecological harm can vary in

degree, ranging from being catastrophic, largely

acute lethal effects on invertebrates, fish and

wildlife, to being longer term or chronic sub-lethal

and cumulative effects. The latter remain a concern,

especially in relation to continuous discharges of oil

from ships onto water surfaces, with lethal and sublethal effects on long-lived, slow-breeding wildlife

such as seabirds (e.g. Wiese 2001, Wiese et al. 2002,

2003). Some shipping incidents, particularly accidents causing large spills, cause widespread community, political and industry concern (NRC 1985;

GESAMP 1993; Mitchell 1993; IMO 1998a) and are

very costly. Recent examples include the Erika (off

France, 1999) and the Prestige (off Spain, 2002),

both of which caused costly cleanups and much

damage to coastal resources. 

3 Hence, there is a strong scientific, economic

and public policy rationale for industry, governments

and agencies to continue efforts to reduce inputs of

oil into the marine environment from all ship-based

sources. As part of the effort to bring attention to the

oil pollution issue and to continue to reduce inputs,

an independent and current assessment of inputs of

oil into the sea from the various sources is required. 

1.1 Scope of task

4 The National Research Council of the United

States published reports in 1975, 1985 and 2003,

estimating the amounts of oil entering the marine

environment from a wide range of sources, e.g. as

land-based effluent releases and run-off as well as

from marine transportation and offshore activities,

including accidental spillages (NRC 1975, 1985,

2003). In 1990, the United States Coast Guard

requested the Marine Board of the National Research

Council to produce an “Update of Inputs of

Petroleum Hydrocarbons into the Oceans due to

Marine Transportation Activities”. The unpublished

report, entitled “Petroleum in the Marine

Environment”, was distributed as IMO document

MEPC 30/INF.13 of 19 September 1990 (MEPC

1990). The most recent NRC report focuses on North

American oil inputs, and oil fates and effects (NRC

2003). 

5 GESAMP6

, when preparing its report “Impact

of Oil and Related Chemicals and Wastes on the

Marine Environment” (GESAMP 1993), used the input

data estimated by the National Research Council in

the 1970s and 1980s, and in the 1990 report to

MEPC, as well as current literature. GESAMP evaluated considerable data and information from the literature on tar or tar balls, i.e. weathered oil accumulations, primarily found on beaches and along coastlines. The occurrence of coastal tar appeared to be

substantial, both in quantity and global distribution.

This showed that considerable oil presumed to be

largely from shipping or ship-based activities were

still entering coastal waters, and that this input might

not be fully accounted for in the input estimates

reported by GESAMP (1993).

6 The Marine Environment Protection

Committee (MEPC) of IMO, at its 35th session in

1994, noted that the estimates made by the National

Research Council in 1990 were based on the

assumption that ships flying the flag of, or registered

in, a State party to the MARPOL 73/78 Convention

would fully comply with its requirements, i.e. it would

apply all provisions prescribed in that Convention.

MEPC requested GESAMP to evaluate all available

data sources on input(s) of oil into the marine environment from sea-based activities, i.e. those related

to shipping and offshore activities, and to develop

approaches that might in future be used for the provision of input data (GESAMP XXVIII). In light of the

many efforts made by IMO to prevent, through a

number of globally applicable conventions, the pollution of the sea by oil from ships, the

Intergovernmental Conference to Adopt a Global

Programme of Action (GPA) for the Protection of the

Marine Environment from Land-based Activities

(Washington, D.C., 23 October - 3 November 1995)

also recommended that IMO should, inter alia, evaluate the input into the sea of oil from all sources.

After consideration by the Fourth Session of the

Commission on Sustainable Development in early

1996, this recommendation was included in a draft

resolution on institutional arrangements for our the

1 INTRODUCTION

6 GESAMP is described on the GESAMP website

(www.gesamp.net) and by Wells et al. (2002).
2 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

implementation of the Global Programme of Action

and submitted to the United Nations General

Assembly at its fifty-first session in December 1996.

The United Nations General Assembly adopted resolution 51/189 on “Institutional arrangements for the

Global Programme of Action”regarding land-based

activities.

7 The IMO Assembly at its twentieth session in

November 1997 took note of the United Nations

General Assembly resolution, indicating that the

degradation of the marine environment from landbased activities was outside IMO’s mandate and that

without extra-budgetary financial resources, IMO

was not in a position to carry out the tasks as set out

in United Nations resolution 51/189. The Assembly

welcomed, however, the information that GESAMP

would, as requested by MEPC, start work in 1997

with regard to the input of oil from sea-based activities, i.e. maritime transportation and offshore exploration and production activities.

8 The first meeting of the GESAMP Working

Group on Estimates of Oil Entering the Marine

Environment from Sea-based Activities was in

November 1997. In this regard, the Working Group

used the term “sea-based activities”. This referred

to Agenda 21 of the 1992 United Nations Conference

on Environment and Development (UNCED) which in

Chapter 17 “Marine Environmental Protection”

(Integrated management and sustainable development of coastal and marine areas, including exclusive economic zones) clearly differentiates landbased activities from sea-based activities. Seabased activities comprise activities related to shipping, dumping, offshore exploration and production,

and the operation of port reception facilities.

9 GESAMP at its twenty-eighth session

(Geneva, April 1998) adopted terms of reference for

the work on oil inputs as follows:

.1 to estimate current annual amounts of oil

entering the marine environment from sea-based

activities, taking into account that:

.1 “oil” would be defined as in MARPOL

73/78, Annex I (IMO 1997), i.e. oil means

petroleum in any form including crude oil,

fuel oil, sludge, oil refuse and refined products (other than petrochemicals);

.2 sea-based activities would include all

forms of shipping, especially in oil tankers

and carriers, other commercial and noncommercial ships, as well as transportation

through marine pipelines. They would further include offshore and coastal exploration

and production, atmospheric emissions from

such sea-based activities, coastal refineries

and storage facilities, oil contaminated

material disposed of at sea, and natural

marine oil seeps;

.3 the annual input estimates would consider both historical and extant data, the

methods for deriving those estimates, and

associated uncertainties; and

.4 the annual input estimates would consider the amounts of oil entering the sea

through operational discharges and accidental spills in relation to quantities transported

by ships, through pipelines, etc., or in relation to offshore and coastal oil exploitation,

and related industrial operations.

.2 to focus particularly on improving the estimates of oil entering the marine environment

from transportation sources, as one test of the

efficacy of the MARPOL 73/78 Convention, and

other conventions where appropriate, pertaining

to the prevention of marine pollution from oil,

and the safety of life at sea.

10 Five meetings of the working group followed,

in May 1998 (Meeting 2), January 1999 (Meeting 3),

February 2000 (Meeting 4), February 2001 (Meeting

5), and February 2003 (working session/meeting 6).

The report was then completed by correspondence,

in Halifax and London.

11 A number of terms e.g. oil, oil discharge,

accidental spills, spills, operational discharge, are

used consistently throughout this report. Definitions

are in the Glossary (Annex).

1.2 Overview of the report

12 The report has four major sections -

approaches to making estimates of oil inputs (Part

2), oil inputs from ships (Part 3), oil inputs from offshore exploration and production (Part 4), and other

oil inputs and related topics (Part 5). The report’s

emphasis is on Parts 2, 3 and 4. The data on oil

inputs (Parts 3-5) are compiled and evaluated to produce a ‘global annual estimate’ for each type of ship

and ship-based activity. The data are then summarized to produce a ‘total global annual estimate’

accounting for all oil inputs from ships and shipbased activities (Part 6). 

13 The general approach and types of inputs

are illustrated in Figure 1 - Framework for Evaluating

Inputs of Oil in the Sea from Sea-Based Activities.

All key sources of data and information are in the

Bibliography. 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 3

2.1 The general approach

14 Obtaining reliable, up-to-date data on quantities of oil entering the marine environment, from all

of the different ship and other sea-based sources

world-wide, is not a simple task. Few countries and

organizations have reliable databases, thus this

report relies heavily on data available for the North

Sea region and for North America. Data on inputs

are lacking from key oil-producing areas such as the

Middle East, South America (e.g. Brazil), West Africa

and South East Asia. As well, there is a difference in

the reporting of oil spilled from the different sources,

which influences the accuracy of the amounts

reported lost; for example, oil lost from shipping

accidents generally includes the slick, oil in the

wreck, and oil burnt, with prior knowledge of the

total amounts in each ship, whereas for oil well accidents or blowouts it is more difficult to estimate what

has been lost to the water and the air.

15 Further problems regarding input data relate

to the fact that changes are taking place continually

in shipping fleets, such as ship design and tonnage,

and in volumes of crude oil transported. Newer

ships are cleaner. Volumes of oil originating from different countries are not constant (e.g. note the

effects of the Venezuelan political crisis in December,

2002 on reducing oil shipments from that country,

and the effects of the Iraq war in Spring 2003 on

reducing oil output from that country). Such

changes and events have to be taken into account

when calculating inputs of oil into the marine environment from ship operations, the predominant seabased activity.

2 METHODS - MAKING ESTIMATES OF OIL ENTERING THE

SEA FROM SHIPS AND OTHER SEA-BASED ACTIVITIES 

Figure 1. Framework for Evaluating Sources of Inouts of oil in the Sea from Sea-based Activities

Oil tankers

Non-oil tankers?

Tankers

Non tankers

Tanker

Non-oil tanker

Non tanker

Loss from onboard bunker

operations & engine

operating

Loss during loading &

transport & COWs

Tank washing

Oil in ballast water

Tankers

Other vessels

Tankers

Combined carriers

Bulk carriers

Royal vessels

Military vessels

Research vessels

Coastguard

State-owned vessels

3.5 Operational discharges from ships

under sovereign immunity

3.5 Scrapping of vessels

3.4 Dry docking of ships

3.2 Operational discharges – cargo

related

3.1.6 Air emissions (VOCs)

3.1.4 Oily ballast from fuel tanks

3.1.3 Fuel oil sludge

3.1.2 Machinery space bilge

3.1 Engine room discharges

Ships operational discharges

Tankers

Barge spills

Tanker spills

Vessels

3.7 Discharges ofoil to

save life at sea

3.3.5 Sunken vessels Accidental spills from

ships

Other vessel spills

Merchant vessel

casualties

Military vessel

casualties

Vessel spills
4 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

16 It should be noted again that “oil” is defined

as in MARPOL 73/78, but many kinds of mineral oils

are considered under this topic. In this study, we

have quantified the oil inputs as “metric tonnes of

oil”, but in so doing, have added together the

weights, or transformed the volumes to weights, of

quite different oils and oily mixtures. The proportions of oil from different sources lost to the sea are

also quite different, as shown in the report. There

are far more small spills of different sorts than large

accidental spills, which are largely crude and marine

fuel oils6(such as bunkers). This distinction is quite

important when considering how to use the information on oil inputs, as ecologically, a tonne of waste

machinery space oils may not equate in potential

impact to a tonne of a light crude or a marine fuel

oil7. Likewise, we can obtain reasonable estimates of

large spills or legal discharges, whereas illegal discharges are rarely quantified. The working group

had many discussions on these points, but considered that taking the “total weight” approach for each

source, normalizing for quantity but not type, was

the only way to produce a summary input value.

17 Oil is a very complex mixture of substances

and as a consequence, its measurement in environmental samples will be a function of the analytical

method used. Although analytical methods are frequently standardized at a national and regional level,

care needs to be exercised in cross comparison of

data. 

18 The physical state of oil in water also affects

its accurate determination in the various environmental compartments. Current methodology

extracts and quantifies hydrocarbons dispersed in

the aqueous phase. The dissolved phase will typically contain low molecular weight aromatic compounds, carboxylic acids and phenols. Estimates of

the concentrations of these groups of substances

have been given in the Exploration and Production

(E&P) Forum, 1994 (E&P Forum 1994). For the North

Sea, concentrations of carboxylic acids have been

measured in the range 100 to 1000 mg l-1 and phenols in the range 1-15 mg l-1. Concentrations of low

molecular weight PAHs are higher in discharges from

gas installations (up to 300 μg l1), while discharges

Figure 1. (cont'd)

4.1.2 Machinery space discharges

4.1.2.2 Drillings discharges

4.1.3 Produced water discharges

4.1.4 Air emissions (VOCs)

Platforms

Wells

4.1 E&P – Operational

discharges

Rigs

4.3 E&P – Pipeline discharges

and spillages

E&P: Operational discharges &

accidental spills

4.2 E&P – Accidental spillages

4.3.2 Accidental releases

4.3.1 Operational discharges

5.1.1 Operational

discharges from

coastal refineries

5.1.2 Accidental

spillages from coastal

facilities

5.2 Reception

facilities

5.3 Oil in waste

dumped at sea

5.4 Fuel dumps from

aircraft

5.1 Coastal refineries

total operational and

accidents

Ships –

operation discharges

5.5 Outboard motors

Ships –

accidental spills

GRAND TOTAL of

inputs in the marine

environment from seabased activities

E&P: Operational

discharges &

accidental spills

Total related fields

5.8 Inputs from

unknown point

sources

5.7 Rocket launches

5.6 Natural oil seeps

5.5.1 Leisure craft

activity

Total other sources

7 Reference should be made to the section on marine fuels

found in Table 2 of ISO 8217:1996. Terms such as Bunker C,

though commonly used in the marine environmental literature, have been replaced since 1980 by new categories of

fuel types. (T.J. Gunner, pers. comm.).
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 5

from oil platforms are generally <10 μg l-1. Similar

constraints on comparability occur in the estimate of

oil based mud (OBM) where the analytical method

used for estimating oil on cuttings will reflect to an

extent the composition and physical partitioning of

the mud components.

19 The challenges notwithstanding, this report

describes the study methods and presents new estimates of annual average global oil inputs from seabased activities, expressed as annual quantities of

oil in metric tonnes (i.e. tonnes/yr.). This report complements the recent report of the United States

National Research Council that largely considered

North American oil inputs (NRC 2003).

2.2 Limitations and uncertainties of

methodology – inputs from ships 

20 Owing to extensive legislation and the fragmentation with regards to vessel type, function, performance and regulatory requirements, this section

was extensively modelled. Different methodologies

from both the original 1990 Report (MEPC 1990) and

between the various sources of oil discharge from

ships have been used in the current report. Given

that cargo-related discharges, bilge oil and fuel oil

sludge are the most extensively analysed, summary

versions are given below.

2.2.1 Operational discharges – cargo-related

21 In the 1990 report (MEPC 1990), the statistics on oil movements by sea were used as a basis

for the remaining estimates and assumptions.

Furthermore, certain intra-area movements of oil at

sea were estimated. On updating the figures for this

report, the amount of oil moved and the tonnage

type and voyage frequency gave a disproportionate

ratio. In this case the total amount of oil moved was

seen as an underestimate owing to the amount of

tonnage in the world fleet. Due to the lack of complete data for intra-area movements8 and owing to

the potential for one cargo to be carried by a number

of vessels, the numbers of tankers were used as the

basis of the estimates of oil transportation and subsequent, cargo related, operational discharge.

22 Due to MARPOL 73/78, various regulatory

requirements apply to varying sizes and types of

tankers hence the quantity of oil discharged from the

various types of tankers will differ. The data are,

therefore, arranged within certain categories to take

into account the various regulations and the current

standard size categories used in the tanker market.

2.2.2 Operational discharges – ship-related (bilge

oil and fuel oil sludge)

23 In estimating the fuel sludge discharge figures for all ships including tankers, it was necessary

to estimate at the outset the bunker consumption for

all ships. This total consumption was then divided

by the sludge component based on fuel testing figures. In the 1990 Report (MEPC 1990), the ship categories were divided between tankers and all other

ships. In order to be more specific in this study, further division of vessels was required as shown in

section 3.1.2.

24 Given the average BHP (brake horse power)

and calculating the number of days at sea for each

category of ship, the total bunker consumption per

vessel was estimated. This was further based on a

bunker usage of 128 grams per BHP per hour (188

grams/kWhr).

25 Sludge generation is based on the sludge

content in the fuel used by each ship. Fuel analysis

companies, FOBAS and DNVPS, suggest that sludge

percentage stands at 0.8%9

. Some fuels are less

likely to sludge, such as marine diesel oil (MDO),

owing to emission regulations. This sludge may also

be incinerated, or delivered ashore, hence its constituent hydrocarbons would not be entering the sea

directly.

26 The sludge production figure of 0.8% was

derived from the bunker consumption figures. An

adjustment was then made to the compliance figure

derived from IMO Port State Control (PSC) detention

statistics, the variability of which was unknown to

the working group.

2.2.3 Air pollution from ships

27 The amount of volatile organic compounds

(VOCs) emitted from oil and chemical tankers, and

returning to the sea surface and water column, has

been very difficult to estimate until recently, because

the phenomena have not been sufficiently studied.

The loss of VOCs from engine/bunkering operations

in all ships has also been impossible to estimate due

to lack of data.

2.3 Accidental spillage methodology

2.3.1 International Oil Spill Database (IOSD)

28 Much of the data used in the analysis of

spillages from all point sources, including vessels,

pipelines, facilities, and offshore exploration and

production activities, are derived from records of

7,400 documented oil spill incidents involving more

than 10,000 US gallons (an arbitrary volume used in

the US to denote a major spill, and equivalent to 34

tonnes) in the International Oil Spill Database (IOSD)

of Cutter Information Corporation, and approximate8 Another way of accessing accurate ship intra-area movement data would be through shipbrokers, such as Fearnleys.

9 This figure and approach can vary. In recent Norwegian

reports (Skjolsvik, pers. comm. July 2003.), evaluating the

production of oily waste in three ships (one bulk carrier, one

tanker, one car carrier), “all vessels either burned sludge in

the incinerators or delivered this ashore. For two of the vessels, the sludge amounted to approximately 0.5% of fuel

consumption, for one vessel 1.4% of fuel consumption”. The

figure used in our study of O.8% is between these values,

and it was assumed that what was generated was discharged to the sea.
6 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

ly 250,000 records of spills of all sizes in the

Environmental Research Consulting (ERC) databases10. The spill data on spills of 34 tonnes and larger

in the IOSD are derived from weekly reports in the Oil

Spill Intelligence Report and information obtained

from sources worldwide representing governmental

agencies, international authorities, non-governmental organizations, and industry. The data in the ERC

databases are obtained from published reports (e.g.

DeCola 2001; Etkin 1996 a,b, 1997 a,b; 1998 a,b;

1999 a-j; Welch 1990, 1991, 1993, 1994, 1995),

Lloyd’s Casualty Archive, reports of spills in periodicals and journals (e.g. Oil Spill Intelligence Report,

Oil Pollution Bulletin, Marine Pollution Bulletin, and

Proceedings of the International Oil Spill

Conference), reviews of large numbers of additional

published lists of spills, regional spill reports, individual spill case studies, data obtained from existing

databases developed by a number of national,

regional, state and provincial authorities, and industry sources, and information obtained from government and industry contacts by a large number of

national fora.

29 Each of the databases contains as much

information as is known and available on individual

spill incidents11. This includes information on spill

date, location, source type, source name, and the

amount and type of oil spilled. This data used for this

study was up to date to the late 1990s.

30 The data involving spills less than 10 tonnes

are considerably less complete and reliable than for

larger spills. The most reliable data for all sources

with the exception of tankers and tank barges

involve spills of at least 34-50 tonnes. Data on all

tanker spills and barge spills, particularly those due

to accidents (groundings, collisions, and allisions)

are better documented and more comprehensive,

due largely to the efforts of the International Tanker

Owners Pollution Federation (ITOPF).

31 Much of the data in the US-based IOSD and

ERC databases was originally recorded in or converted to units of US gallons. Since most international authorities and non-US national authorities

rely on the metric tonne for oil measurement, the

metric tonne (referred to in this study as the tonne)

was used in this analysis and all volume measurements have been converted to tonnes for simplicity

of comparison.

32 The conversion of US gallons to tonnes

involves the conversion of a volumetric measure (gallon) to a mass measure (tonne). The measure of the

volume of oil can itself present inaccuracies since oil

has different volumes depending on its temperature. 

For truly precise conversions from gallons to tonnes,

it is also important to take into account that different

oils have different relative densities. For this reason

it is necessary to use relative density (the density in

relation to pure water) in making conversions such

that:

US gallons = (921.5 x tonnes)/(3.785 l/gal x relative density).

Eqn. 1.

33 Relative densities of petroleum products

generally range from approx. 0.74 for gasoline, to

approx. 0.90 for a heavy crude, and to 0.95 for a

heavy marine fuel (formerly known as a Bunker C or

No. 6 fuel oil) (Clark and Brown 1977; NRC 1985;

Etkin 1999i). Some heavy blends of marine fuels are

even heavier than seawater, having relative densities

over 1.0. In all analyses of accidental spills, the conversion of volumes of oil to tonnes of oil is based on

an average relative density of 0.83, an average

measure of a number of different oils including various crude and fuel oils (Etkin, pers. comm.). This

results in 294 US gallons per tonne of oil12

.

34 Data on spill incidents in the IOSD and ERC

databases, as well as other compiled data on which

these databases rely, are collected from a large number of credible sources on an international basis.

Due to the nature of the data collection process, discrepancies and inaccuracies exist in these databases and original data sources. For example, incident

information can be inaccurate regardless of its

source; one recent spill in Korea was reported by a

reputable news agency as >20,000 tonnes, whereas

it was actually 2-5 tonnes (ITOPF, pers. comm.). As

well, there are undoubtedly omissions of spills, especially those in smaller size ranges and from areas in

which spill recording and reporting are not rigorously pursued; the percent error for the various input

categories due to omissions is unknown. Hence,

spill input figures are smaller than the “true” values.

35 Prior to the 1970s, reporting of oil spills to

authorities and record keeping on oil pollution was

not legally required in many countries, including the

US. Although major spills during this earlier period

(1950s and 1960s) have been logged, input data

prior to the 1970s should be viewed with caution and

the values taken as underestimates. The data prior

to the 1980s in the IOSD and ERC databases are

particularly incomplete with regard to spills from

non-vessel sources; these spills tended to escape

the notice of media and the public unless they were

in highly visible or high profile locations, such as in

the vicinity of amenity beaches (e.g. cities or

resorts). Even in recent years, reporting of oil spills

and sharing of information on spill events from some

countries and regions have been unreliable for both

political and logistical reasons. In some countries,

record keeping and reporting requirements have

been less rigorous in the past and spillage records

10 The IOSD and ERC databases are not in the public domain.

However, this study and that of the recent NRC Committee

(NRC 2003) relied on their data. The databases are acknowledged to be the best available, due to the specialty of the

firms and their experts. The proprietary nature of the two

databases precludes other independent analysis of the input

data.

11 The ITOPF database on tanker spills is also very extensive

but was only selectively utilized for this study.

12 GESAMP (1993) reported 308 US Gal. or 1,165.78 litres, per

metric tonne for typical crude oils, a higher conversion factor than used in this study due to it being derived solely from

crude oils.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 7

often have been incomplete. In general, however,

reporting of spill incidents has improved worldwide.

36 The analyses of accidental spillages are subject to these inherent deficiencies in the data, and all

input estimates for accidental spills should generally

be viewed as underestimates.

2.3.2 Estimation factor for smaller spills

37 In any one year and in any one location,

many more small spills occur than very large spills,

i.e. small spills contribute a large percentage of the

total number of spills annually. At the same time,

even added together, the smaller spills contribute a

much smaller amount of oil spilled than one much

larger incident.

38 The spillage represented by these smaller

spills could be merely accepted as a weakness of the

data. However, for calculating the amount of oil

spilled annually in the marine environment from

these spills, it is important to include as much information as possible in the estimation attempts.

Likewise, for the purposes of analysing the efficacy

of prevention measures and the risks for ecological

effects, it is important to consider the total number

of incidents, including these smaller spills.

39 The IOSD contains no verified information on

oil spills below 34 tonnes and the ERC databases

contain incomplete information on oil spills in this

smaller size range. Hence, a “small spill estimation

factor” was calculated by D. Etkin (ERC) for both the

number of spills and the amount of oil spilled in incidents involving less than 34 tonnes. The two estimation factors (for number of spills, and amount spilled)

were based on an analysis of over 95,000 spills of at

least one US gallon (0.003 tonnes) that occurred in

US marine waters during 1985-1999. The data are in

the ERC database based on comprehensive data of

spills of at least one US gallon (0.003 tonnes) from

the US Coast Guard, the US Minerals Management

Service, Environmental Protection Agency, the US

Office of Pipeline Safety, and several State databases; they were compiled, cross-checked and verified.

The ERC data set was selected since it was the most

complete set of data available to the working group

and lent itself to rigorous statistical testing.

40 A frequency distribution analysis was conducted on over 60,000 vessel spills and nearly

35,000 pipeline and facility spills in US marine

waters to derive correction factors for vessels and

for coastal and offshore pipelines and facilities. 

41 The application of the small spill estimation

factors derived solely from US data to correct the

missing of representation of small spills introduces

inherent errors. The pattern of spillage in different

regions of the world may not follow the frequency

distribution of spill sizes in the US data, although it

would be expected that small spills are generally

more common than larger spills in all areas. Even

within the US data set, the frequency distribution of

spill size varied from year to year. 

42 The frequency distribution analyses of the

US data are shown in Figures 2 and 3. Final small

spill estimation factors for both vessels and

pipelines/facilities were calculated by taking the percentage of the number of oil spills under 34 tonnes

and the total amount of oil spilled in spills involving

less than 34 tonnes but at least 0.003 tonnes (the

equivalent of one US gallon). Thus, an average of

23.3% of the total amount of spilled oil from vessels

is spilled in incidents of less than 34 tonnes,

although this represents 99.99% of the number of

incidents. For pipelines and facilities, 17.4% of the

total amount of oil spilled comes from incidents

involving 0.003-34 tonnes. The smaller spills comprise 99.6% of the total number of pipeline and facility spills. 

43 To project from the international data on

spills of over 34 tonnes to the larger range of spills

involving at least 0.003 tonnes, the small spill estimation factor for spill number was applied in the following manner for vessels:

Vnl = 0.001 x Vne

or

Vnl/0.001 = Vne

where Vnl = number of vessel spills ≥ 34 tonnes; Vne =

estimated number of vessel spills ≥ 0.003 tonnes.

This estimation assumes that if there are x vessel spills of at least 34 tonnes, then there are an estimated 1,000 x spills of at least 0.003 tonnes. It

should be noted that this estimation applies to all

vessels and for all types of spill causes.

Figure 2.

Cumulative Percentage of Total Oil Spillage From

Facilities and Pipelines Into US Marine Waters

(Numbers of Spills and Amounts) By Size Class US

Vessel Spills (1985-1999) (Environmental Research

Consulting Database)

Figure 3.

Cumulative Percentage of Total Oil Spillage From

Facilities and Pipelines Into US Marine Waters

(Numbers and Amounts Spilled) By Spill Size Class

(1985-1999) (Environmental Research Consulting

Database)
8 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

44 Likewise, to estimate the amount of oil

spilled from vessels in all size classes based on verified data of spills of at least 34 tonnes, the following

estimation factor was applied:

Val = 0.767 x Vae

or

Val/0.767 x Vae,

where Val = amount spilled from vessels in spills ≥ 34

tonnes; Vae = estimated amount spilled from vessels

in spills ≥ 0.003 tonne.

This estimation states that, if there are x tonnes

of annual spillage from vessels attributable to spills

involving at least 34 tonnes, there are an estimated

1.3x tonnes of oil spilled in incidents involving at

least 0.003 tonnes.

45 For coastal pipelines and facilities (including

offshore exploration and production facilities), a second estimation factor for spill numbers was derived

as follows:

PFnl = 0.004 x PFne

or

PFnl/0.004 x PFne,

where PFnl = amount spilled from pipelines and facilities in spills ≥ 34 tonnes; PFne = estimated amount

spilled from pipelines and facilities in spills ≥ 0.003

tonne.

This estimation states that, if there are x number

of pipeline and facility spills of at least 34 tonnes,

there are an estimated 250x spills of at least 0.003

tonnes. It should be noted that this estimation

applies to all pipelines and facilities and for all types

of spill causes.

46 Another estimation factor for spill amount

was derived for application to pipeline and facility

spill input estimates, as follows:

PFal = 0.826 x PFae

or

PFal/0.826 = PFae,

where PFal = amount spilled from facilities/pipelines

in spills ≥ 34 tonnes; PFae = estimated amount spilled

from facilities/pipelines in spills ≥ 0.003 tonne.

This estimation states that, if there are known to

be x tonnes of annual spillage from pipelines and

facilities attributable to spills involving at least 34

tonnes, there are an estimated 1.21x tonnes of oil

spilled in incidents involving at least 0.003 tonnes.

2.3.3 Application of the small spill estimation

factors to the IOSD

47 To project from the IOSD data of spills over

34 tonnes to the larger range of spills involving at

least 0.17 tonnes, the small spill estimation factor for

spill number was applied in the following manner:

IOSD spill number = 0.03203 x estimated number of

spills ≥ 0.17 tonnes

or

IOSD spill number/0.03203 = estimated number of

spills ≥ 0.17 tonnes

48 Likewise, to project from the IOSD data of

spills over 34 tonnes to the larger range of spills

involving at least 0.17 tonnes, the small spill estimation factor for spill amount was applied in the following manner:

IOSD spill amount = 0.84408 x estimated amount

from spills ≥ 0.17 tonnes

or

IOSD spill amount/0.84408 = estimated amount from

spills ≥ 0.17 tonnes

2.3.4 Average annual input estimation

49 Preliminary estimates of average annual

input for the time period 1988-1997 were made for

all source categories of accidental spills by taking

the mean estimated annual spill amount based on

the amount spilled in incidents involving at least 34

tonnes adjusted upwards to account for the estimated amount of spillage that would be attributable to

spills of at least 0.003 tonnes to just under 34

tonnes. These figures were compared to estimates

for the two previous ten-year time periods (1968-

1977 and 1978-1987) that were made using the same

methodology and data sets.

50 Deriving an average annual input figure for a

ten-year period presents a statistical problem in that

there is considerable variability from one year to the

next in terms of the amount of oil spilled from the

various sources. In any year, one or more very large

(over 5,000-tonnes, arbitrarily set by US) spills can

completely dominate the annual input for that year

(see Figure 4). The estimated annual input figures,

therefore, need to be put into perspective by adjusting for these very large inputs.

51 The annual percentage of vessel spills

involving 5,000 tonnes or more has declined considerably since 1968 (see Figure 5 and regression equation), but has remained steady at about 0.2% of

spills for the last decade. Thus, on average in any

one year, 0.2% of accidental vessel spills involve at

least 5,000 tonnes of oil (e.g. Khark V in 1989, ABT

Summer in 1991, see Table 21). With the exception

of 1995, which experienced no spills in this size category, all years in the last decade have involved at

least two spills of this magnitude. In fact, over the

last decade the average number of spills involving

over 5,000 tonnes is 4.1 spills annually.

52 Another approach to estimating average

annual input from accidental releases would be to

look at average annual spillage without these larger

spills and then to add the larger spills as an error or

uncertainty factor. This would give a more accurate

perspective on the current state of affairs with

respect to accidental spillage. The variability from
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 9

year to year of total spill amount attributable only to

spills below 5,000 tonnes has varied relatively little

over the last decade (see Figure 4). Applying a separate factor of spill amount over 5,000 tonnes is

most appropriate for vessel spills of all the source

categories since, historically, the great majority of

spill incidents in this size category have involved

vessels. During the time period of 1988-1997, 93%

of incidents over 5,000 tonnes involved tankers and

barges; the remaining 7% were pipeline incidents.

53 Extremely large exploration and production

activity spills such as the Ixtoc I well blowout spill of

1979-1980, which involved the spillage of in excess

of 476,000 tonnes of oil, are even rarer than very

large tanker spills. The Ixtoc I spill, though a rare

event, represented the largest total amount of oil

released from a single, man-made point source in

recorded history. While the probability of another

extremely large blowout has been vastly reduced by

current methodologies and technology, the possibility still exists and should be borne in mind in making

any kind of predictive analyses. There were no

exploration and production spills over 5,000 tonnes

during the 1988-1997 period designated for the input

analysis of this report.

54 Spills attributable to war-related events can

also be extremely large. The spillage into the Gulf

during the 1991 Gulf War of an estimated 986,000

tonnes due to attacks on eight tankers and 13 facilities is such an epochal event. This could be repeated, though speculation on the probability of this type

of war-related occurrence is beyond the scope of

this study. Any individual Ixtoc I- or Gulf War-type

event or series of such events would greatly skew

the input data and resulting analyses for any decade

or individual year. Due to the unique circumstances

surrounding spills related to war attacks, these spill

events were removed from the accidental spill data

and are presented separately.

55 Estimates of accidental spillage from the

various sources were calculated as the average

annual amount attributable to spills of less than

5,000 tonnes and the average annual amount spilled

in incidents involving 5,000 tonnes or more. The

average annual input estimate for each accidental

spill source type was then calculated using the

amount spilled in incidents involving less than 5,000

tonnes plus the average annual amount attributed to

spills in the larger spill size category. 

2.3.5 Definition of accidental spillage

56 In the context of this study and in all ensuing

analyses of “accidental” spillages, the term “accidental” does not necessarily imply that there is no

fault or possible intent involved in all of the included

incidents. The “accidents” should be viewed as

“incidents” involving the release of oil from point

sources over a relatively limited amount of time (i.e.

hours or days), rather than from slow leakages of relatively small amounts of oil over months or years. An

exception to the criterion of a time limit would be the

inclusion of the 1979 Ixtoc I well blowout in the Gulf

of Mexico that caused the discharge of large

amounts of oil over a period of ten months.

Figure 4.

Accidental Oil Spills from All Source Types into the

Marine Environment (1988-1997) (ERC Database

and OSIR International Oil Spill Database)

Figure 5.

Percent of Vessel Spill Numbers Involving at Least

5,000 Tonnes of Oil (Based on Etkin 1999h)

57 Most accidents are unintentional (see glossary). However, the “accidents” that are used in this

analysis include spills that may have been intentional. These include the 149 incidents over 34 tonnes

which involved the intentional release of oil, the case

of illegal discharges of amounts of oil in excess of

that which can be expected from vessels in operational discharges of not more than 15 ppm in the

manner described in MARPOL 73/78, and the jettisoning of oil to prevent loss of life at sea. Legal

operational discharges are covered in section 3.1 of

this report. An additional 77 incidents involved war

acts resulting in the spillage of oil from vessels, and

50 incidents involved war acts resulting in spillage

from exploration and production (E&P) facilities,

coastal facilities, and pipelines. “Accidental”

spillage, then, is defined as the release of oil,

whether intentional or unintentional, from a point

source in one incident over a limited period of time

other than what could normally be expected as operational or MARPOL-regulated discharges.

2.3.6 Regional analysis of accidental spillage data

58 The data on accidental oil spills derived from

the International Oil Spill Database (IOSD), with the

small spill estimation factors for spills under 34

tonnes, were analysed on a regional basis for 18

regions (See Figs. 5 and 6, also Etkin 1999g).

59 The 18 regions (Figure 6) selected for analysis were based on approximate boundaries of marine

areas defined by the UNEP Regional Seas
10 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Programme as well as special areas described under

MARPOL 73/78, within the geographic selection limitations of software programmes based on 10-degree

Marsden squares. The areas not covered by either of

these descriptions were based on arbitrary subdivisions of remaining marine areas. The boundaries of

the regions used in these analyses are shown in

Table 1. The boundaries to these regions are not

based on any national boundaries or territorial

waters and no implications were made with regard to

any particular countries with respect to oil spillage.

Indeed, several countries are represented in two

areas since the regions selected were based on seas

or ocean regions rather than on national boundaries.

Data on individual regions should be viewed very

carefully with this in mind.

60 Each region was analysed for spillage over

the course of the last three decades (1970s to 1990s)

for both numbers of spills and total amount of

oil spilled. As with all the data analyses based on

the databases with the small spill estimation

factors applied, there are inherent inaccuracies in

the estimation techniques used to derive these figures.

61 The estimates for average annual input of oil

are based on data of actual spills recorded with

adjustment factors for vessels and pipelines/facilities

for the absence of data on smaller spills. The small

spill estimation factors have been used to increase

accuracy of the data by taking into account the lack

of data on small spills of under 34 tonnes. There

may, however, be unavoidable gaps in records on

spills of over 34 tonnes that might create underestimates in accidental spillage figures even after the

adjustment factors are applied to both spill number

and spill amount. In addition, some regions have

less reliable spill data reporting facilities than others,

which may also lead to underestimation of inputs in

those regions.

62 In addition, the use of the small spill estimation factors (derived from an analysis of United

States data) might create some inaccuracies, especially with regard to spill numbers, if the pattern of

spillage worldwide does not closely resemble the

size frequency distribution of spill sizes in the United

States. In general, however, it can be expected that

spill size frequency would follow a pattern of many

smaller spills and fewer large spills.

Figure 6. Regional oil spill analysis showing the 18 geographic regions (Etkin, 1999g)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 11

Table 1. Regional descriptions for regional data analysis (adapted from Etkin 1999g)

Region

number1 Region name Region boundaries2

1 Northeast East of 170°W, north of 10°N, east to coastal and estuarine areas of USA, Canada, Mexico,

Pacific Ocean Guatemala, El Salvador, Honduras, Nicaragua, and Costa Rica to 10°N

2 Southeast East of 170°W, south of 10°N to 60°S, east to coastal and estuarine areas of Costa Rica, Panama, 

Pacific Ocean Columbia, Ecuador, Peru, and Chile east to 70°W

3 North West of 40°W to coastal and estuarine areas of Canada and USA to east coast of Florida, USA

Atlantic Ocean

4 Gulf of Mexico/ Gulf of Mexico and Caribbean Sea to coastal and estuarine areas of USA (western and souther coast

Caribbean Sea of Florida west to Texas), island nations and territories in Caribbean Sea east of 60°W, eastern

coastal and estuarine areas of Mexico, Belize, Guatemala, Honduras, Nicaragua, Costa Rica,

Panama, and northern coastal and estuarine areas of Colombia; not including Lake Maracaibo area

of Venezuela

5 Southwest West of 20°W to coastal and estuarine areas of Argentina, Uruguay, Brazil, Fr. Guinea, Suriname,

Atlantic Ocean Guyana, Venezuela (including Lake Maracaibo), and Magellan Strait east of 70°W

6 Northeast East of 40°W, north of 30°N to 60°N, east to coastal and estuarine areas of Ireland, United Kingdom,

Atlantic Ocean not including east of 5°W north of Scotland, United Kingdom, or north of 52°N on eastern coast of

United Kingdom or coast of Belgium; including France, Portugal, Spain, and Morocco, west of

Gibraltar

7 North Sea North of 52°N at eastern coast of United Kingdom and coast of Belgium north to 65°N east to 5°W

to Scotland, United Kingdom, coast, and east to 10°E, including coastal and estuarine areas of western United Kingdom, Belgium, Netherlands, Germany, Denmark, and Norway

8 Baltic Sea Baltic Sea, Kattegat, Gulf of Bothnia, Gulf of Finland, and Gulf of Riga, east of 10°E to 30°E; incluing coastal and estuarine areas of Denmark, Sweden, Norway, Germany, Poland, Lithuania, Latvia,

Russian Federation, and Finland

9 Mediterranean East of Strait of Gibraltar, including Mediterranean Sea, Tyrrhenian Sea, Adriatic Sea, Ionian Sea,

Sea Aegean Sea, up to, but not including Bosporus Strait, Turkey; including coastal and estuarine areas

of France, Spain, Italy, Monaco, Greece, Turkey, Syria, Lebanon, Israel, Egypt, Libya, Tunisia,

Algeria, Slovenia, Croatia, Bosnia-Herzogovnia, Yugoslavia, Albania, and Morocco

10 Black Sea Black Sea including Bosporus Strait; including coastal and estuarine areas of Turkey, Bulgaria,

Romania, Georgia, and Russian Federation

11 West/Central African South of 30°N, east of 40°W to 0°, east of 20°W, north of 10°S, east towards western African coast;

Atlantic Ocean including coastal and estuarine areas of Morocco, W. Sahara, Mauritania, Senegal, Gambia, GuineaBissau, Guinea, Sierra-Leone, Liberia, Côte d’Ivoire, Ghana, Togo, Benin, Nigeria, Cameroon,

Equatorial Guinea, Gabon, Congo, Zaire, and Angola north of 10°S

12 Southern Africa South of 10°S, east of 20°W to African coastal and estuarine areas east to 30°E; including Angola

south of 10°S, Namibia, and South America to 30°N on Indian Ocean coast

13 Eastern Africa East of 30°E to 60°E north as 10°N; including coastal and estuarine areas of South Africa north of

Indian Ocean 30°N, Mozambique, Madagascar, Tanzania, Kenya, and Somalia north to 10°N

14 Red Sea/ Red Sea, including Suez Canal, and Gulf of Aden and Gulf of Aqaba, north of 10°N, east to 60°E;

Gulf of Aden including coastal and estuarine areas of Somalia, Djibouti, Eritrea, Egypt, Yemen, Saudi Arabia,

Oman, and Jordan

15 Gulf Gulf area and associated coastal and estuarine areas in Saudi Arabia, Qatar, United Arab Emirates,

Bahrain, Kuwait, Iraq, and Iran, to Strait of Hormuz

16 Arabian Sea/ East of 60°E, and Gulf of Hormuz, east to 100°E; including coastal and estuarine areas of Iran,

Indian Ocean Oman, Pakistan, India, Bangladesh, Burma, Sri Lanka, Thailand, and Indonesia

17 East Asia/ East of 100°E, north of 10°S, east to 170°W; including coastal and estuarine areas of Thailand, 

Southeast Asia Indonesia, Malaysia, Japan, North Korea, South Korea, Vietnam, Philippines, China, Russia, Papua

New Guinea, and Brunei

18 Australia/ East of 100°E to 170°W, south of 100°S; including coastal and estuarine areas of New Zealand and

New Zealand Australia

1 Refers to regions depicted in regional map

2 Boundaries were determined on the basis of approximate marine areas rather than on national boundaries.
12 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

2.4 Produced water discharges

63 Water occurs naturally in geological oil reservoirs and is extracted from formations along with the

hydrocarbons. Production water and hydrocarbons

are separated at the site of production by physical

and chemical techniques. The water phase may be

re-injected into the reservoir to maintain pressure

and thereby to enhance exploitation. At some locations, where the subterranean geology permits, produced water can be re-injected as a means of disposal. However, for geological and other reasons,

this option is not widely available, thus treated produced water containing amounts of dispersed oil is

most often discharged at sea.

64 In the initial stages of exploiting a hydrocarbon deposit, production water volumes may be low.

As the field matures, however, volumes of production

water rise and in mature areas water amounts of

more than 90% are typical.

65 In many producing areas, local and/or

regional regulatory authorities have imposed a quality standard for oil in produced water. Numerical

standards range from around 30 mg oil per litre of

produced water to 100 mg l-1. In others, discharge

targets or standards have not been established. In

all cases, it is clearly in the operators’ interests to

maximize the separation of oil (product) from water,

if only from an economic perspective. Care must be

taken, however, in making direct comparisons

between the numerical standards defined in different

geographic regions. As stated above, since oil is a

complex mixture of organic components, analysis of

oil in water is non-specific and results of determinations will be dependent upon the analytical method

used. Thus, numerical differences in standards do

not necessarily reflect different regional views on

environmental protection. Consequently, for this and

other reasons, care must be taken comparing and

combining input estimates from different producing

regions.

2.5 Operational discharges from coastal

refineries

66 The estimates for operational discharges

from coastal oil refineries due to oily effluents are

based on the total crude refining capacities of

coastal or estuarine refineries as reported by

PennWell Oil Directories (Tippee 2001). The total

worldwide crude oil refining capacity is currently

about 7,800,000 tonnes per day (circa Feb 2001), but

increasing due to demand.

67 Four assumptions were made in assessing

the maximum estimate of input:

.1 that refineries produce, on average, 4.5 units

of wastewater per unit of refining capacity

(shown by CONCAWE and EDF studies);

.2 that refinery effluents contain 5 ppm to 25

ppm of oil, depending on the condition and

operation practices of the refineries;

.3 that refineries operate year-round; and

.4 that refineries discharge the maximum

amount of oil permitted into their effluents.

There is also an implicit assumption that any

effluent discharge that contains more than the permissible oil content should conceptually be considered a spill event rather than a permissible operational discharge.

68 The fact that higher oil levels may consistently be discharged in effluents is recognized. Such

long-term discharges are unlikely to have been captured in spill event data which tracks discrete spill

events rather than long-term small leaks. At the

same time, it is known that many refineries in such

countries as the United States discharge below the 5

ppm threshold (EDF 1995). This over- and underestimation of effluent oil content is a source of error

in the overall input estimates. At the same time, the

assumptions above do not always hold true. All

refineries do not operate year-round at full capacity

(D. Etkin, unpubl. data). The actual number could be

as low as one quarter to one half of this amount if the

less efficient refineries were actually releasing less

than 25 ppm of oil in their effluents and were operating on a less than full-time schedule. The estimated

input numbers for refinery operational discharges are

put into a range to reflect this uncertainty. 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 13

3.1 Operational discharges – shiprelated 

3.1.1 Introduction

69 Operational discharges of oil into the marine

environment by ships depend on several factors.

These include: type and age of ship; level of maintenance of ship and engines; presence of oil-water

separators and other equipment designed to curtail

discharges of oil; practice of the LOT (load-on-top)

principle; training and vigilance of the crew; level of

shipping activity, which was lower in the 1990s than

in previous decades13; and presence of adequate

reception facilities. Under the MARPOL 73/78

Convention, Annex 1 (IMO 1997a), discharges of oil

are strictly regulated. As from 1997, the maximum

legal operational discharge of oil was reduced from

100 parts of oil per million parts of water (i.e. ppm) to

15 ppm per nautical mile (nm), beyond 50 nm off a

coastline.

3.1.2 Operational engine room wastes and

discharges (Fuel oil sludge and bilge oil)

70 Tankers generally do not have a storage

problem for excess sludge generated from purification of bunker fuels. The excess sludge and bilge oil

(i.e. oily bilge waters, or oily waters, originating from

engine room) that cannot be stored in the engine

room sludge tank may be transferred to the vessel’s

main slop tanks for subsequent LOT or load on top,

i.e. addition to the oil cargo, or it may be incinerated. However, such a procedure is not available to

those tankers trading with clean products, that is,

9.4% of the total tanker tonnage (see section 3.2);

therefore, the estimations have been corrected

accordingly for these vessels for non-compliance.

71 Sludge and bilge oils are collected in the

engine room sludge tanks and are taken to be the

same source of oil for the estimations in this section.

Due to the high cost of lubricating oil and the

increasing refinement of marine engines, the numbers used in the 1990 report (MEPC 1990) are overestimates based on today’s practices (circa 2002).

For an estimate of the bilge oil fraction, it has been

assumed by Intertanko experts that this would be

1% of the total amount contained in the sludge

tanks. It is further noted under MARPOL 73/78,

Annex VI, that most of the fuel oil sludge produced

goes to the ship’s incinerator, and any remaining fuel

oil sludge would be stored separately and discharged to port reception facilities.

72 On estimating the fuel sludge discharge

numbers for all ships including tankers, it was necessary at the outset to estimate the bunker consumption for all ships. In the 1990 report (MEPC 1990),

the ship categories were divided between tankers

and all other ships. In order to be more specific, a

further division of vessels was required. Table 2

illustrates the division of vessels together with the

number of ships and their average brake horsepower (BHP) taken from the Fairplay database (Fairplay

Database 2000).

73 Given the average BHP and estimating the

number of days at sea for each category of ship (see

Table 2), the total bunker consumption per vessel

was estimated. As stated earlier, this was further

based on the bunker usage of 128 grams per BHP

per hour (see Table 3 below). The calculations gave

a total consumption for all ships of 224,119,523

tonnes/yr. or ~224,000,000 tonnes/yr.14

74 Sludge generation is based on the sludge

content in the fuel used by each ship. Fuel analysis

companies, FOBAS (Fuel Oil Bunker Analysis and

Advisory Service, Lloyd’s Register, London, United

Kingdom) and DNVPS (DNV Petroleum Services,

London, United Kingdom), suggest that sludge percentage stands at 0.8% (Also note footnote 9). A

number of vessels now run on fuels that are less likely to sludge, such as marine diesel oil (MDO), owing

to new emission regulations. This sludge may also

be incinerated, together with the bilge oil waste,

hence, is not directly entering the marine environment.

75 The sludge production number of 0.8% is

applied to the bunker consumption numbers, with

the outflow numbers being estimated using the

MARPOL 73/78 Annex I discharge allowance of 15

ppm. Table 4 illustrates discharge of fuel oil sludge,

calculated on the assumption of 100% compliance.

Based on this total compliance, the annual discharge

into the marine environment of fuel and bilge oil from

all of the ships combined is estimated at 13,453

tonnes/yr, or ~13,500 tonnes/yr.

76 However, IMO estimates on compliance

numbers taken from submissions from States that

are party to MARPOL 73/78 have shown a range of

compliance under Port State Control (PSC) inspections of between 72% worst case and 100% (IMO

FSI 9/8, 2001). On the basis of the median of 86%,

compliance was used as an estimate of compliance

in the shipping section of this report. Table 5 gives

the outflow numbers adjusted for this compliance

percentage.

3 OIL INPUTS FROM SHIPS

13 “Shipping has been through a recession in the 1990s, hence

the annual fuel consumption is not significantly higher now

than in 1990. The discharge regulation is stricter and the

fleet partly renewed. Hence, one would expect a significant

reduction (of oil input) compared to 1990 figures in oil input

from bilge oil discharge.” (K.O. Skjolsvik, pers.comm.).

14 Other studies of total ship fuel consumption globally per year

give other values. “Total world consumption from ships has

been estimated in the range of 200,000,000-270,000,000

tonnes/yr., the number varying with amount of domestic

shipping included in the calculation” (K.O. Skjolsvik, pers.

comm.). Our numbers are in this range.
14 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Table 2. Ship types, numbers and average brake horsepower (BHP)

Ship Type Number of Ships Avg. BHP*

Bulk Carriers 08,680 08,232

Combination Carriers 00,212 14,423

Container Vessels 02,574 20,504

Dry Cargo Vessels 07,446 04,374

Miscellaneous 05,570 04,168

Offshore Vessels 02,903 06,652

Ferries/Passenger Vessels 02,756 10,836

Reefer Vessels 01,838 06,772

RoRo Vessels 01,939 10,275

Tankers - All cats. 08,156 08,857

Total 42,074

*Avg. BHP – average or mean brake horsepower.

Table 3. Estimation of total bunker consumption (cons.) per vessel

Ship Type Number Avg. Daily Bunker Number of Yearly Bunker Total Cons. for

of Ships BHP Consumed* Days at Sea Cons./Vessel Vessel Type

Bulk Carriers 08,680 08,232 25.289 200 05,058 043,901,183

Combination Carriers 00,212 14,423 44.307 200 08,861 001,878,610

Container Vessels 02,574 20,504 62.990 180 11,338 029,184,295

Dry Cargo Vessels 07,446 04,374 13.438 150 02,015 015,009,051

Miscellaneous 05,570 04,168 12.803 200 02,560 014,263,099

Offshore Vessels 02,903 06,652 20.434 200 04,086 011,864,184

Ferries/Passenger Vessels 02,756 10,836 33.288 250 08,321 022,935,349

Reefer Vessels 01,838 06,772 20.803 200 04,160 007,647,164

RoRo Vessels 01,939 10,275 31.564 250 07,891 015,300,591

Tankers - All cats. 08,156 08,857 27.209 280 07,618 062,135,997

Total 42,074 224,119,523

* Bunker consumed (cons.) in tonnes.

Table 4. Discharge of fuel oil sludge from vessels, in tonnes, on assumption of 100% compliance with MARPOL

Annex I

Ship Type Total Oil Consumed Sludge Generation Legal Discharge 100% compliance,

for Vessel Type 15 ppm tonnes discharged

Bulk Carriers 043,901,183 0,351,210 05.27 003,517

Combination Carriers 001,878,610 0,015,029 00.23 00,0151

Container Vessels 029,184,295 0,233,474 03.50 002,338

Dry Cargo Vessels 015,009,051 0,120,073 01.80 001,203

Miscellaneous 014,263,099 0,114,105 01.71 001,143

Offshore Vessels 011,864,184 0,094,913 01.42 000,951

Ferries/Passenger Vls 022,935,349 0,183,483 02.75 001,838

Reefer Vessels 007,647,164 0,061,177 00.92 000,613

RoRo Vessels 015,300,591 0,122,405 01.84 001,226

Tankers - All cat. 062,135,997 0,497,088 07.46 000,475

Total 224,119,523 1,792,956 26.89 013,453
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 15

77 In summary, the estimated total operational

discharge into the marine environment of fuel oil

sludge and bilge oil from all ships = 187,990

tonnes/yr. or 188,000 tonnes/yr. Given the

assumption that 1% of this figure would be bilge oil,

the following components can be derived:

Fuel Oil Sludge into the marine

environment = 186,120 tonnes/yr.

Bilge Oil into the marine

environment = 1,880 tonnes/yr.

Total operational engine room

discharges = 188,000 tonnes/yr.

3.1.3 Oily ballast from fuel tanks

78 The use of fuel tanks for ballasting a ship is

now seen as an option, though it is limited in use and

high in risk. It was noted by MEPC (1990) that certain non-tankers such as fishing vessels may still

continue to use this practice of ballasting.

Information from industry sources states that this

practice is more cumbersome and includes the risk

of mechanical/engine problems due to fuel contamination. As a consequence, this practice is seen as

rare, however, an attempt has been made to take this

into account and update the figures from those in the

1990 MEPC report.

79 In the 1990 MEPC report, 2% of non-tankers

were estimated as carrying out this procedure. This

has been revised down to 1% based on indicators

stressing the limited use of the procedure. The clingage factor had already been revised by the 1990

report and due regard for the use of marine diesel

fuel was given. In this regard, the factor of 0.4% in

the 1990 report has been maintained.

80 Vessels have two options on the discharge of

oily water produced under MARPOL 73/78. Firstly,

in the absence of oily water filtering or separating

equipment, the waste oil should be delivered to

shore facilities and, secondly, discharge is permitted

with the correct equipment at a maximum of 15 ppm.

In view of this requirement, the 1990 report estimated that 25% of the oil waste would be discharged

into the sea. This number can be corrected using the

compliance number derived in section 3.1 and

revised to 14% of the oil waste being discharged.

The following equation takes into account the fuel

consumption numbers developed in section 3.1.1

and gives the estimated discharge into the sea from

ballast in fuel tanks procedure as:

Total tonnage (based on Fairplay Database 2000) x

% non-tankers carrying out this procedure x the clingage factor (%) x quantity discharged based on 14%

(non-compliance).

161,983,545.2 x 0.01 x 0.004 x 0.14 = 907 tonnes.

Oily ballast (fuel tanks) into the marine environment =

907 tonnes/yr.

3.1.4 Total operational discharges – ship-related:

total amount of oil discharged from engine

rooms (all ships)

81 The estimated total amount of oil entering

the sea annually from the engine rooms and fuel

tanks of all ships, based on the above, would be:

Fuel Oil Sludge: 186,120 tonnes

Bilge Oil: 001,880 tonnes

Oily Ballast from Fuel Tanks: 000,907 tonnes

Total: 188,897 tonnes/yr.

or 189,000 tonnes/yr.

3.1.5 Air emissions - VOCs from tankers -

“Volatile Organic Compounds”

82 Oil and certain volatile organic cargoes

release VOCs during loading and unloading operations and transport, and the operation of the ships

themselves results in the release of VOCs from the

engines and funnels (Ostermark and Petersson 1993;

Christensen 1994; APARG 1995; Anon. 1998 d).

VOCs go into the atmosphere and a fraction returns

to the sea surface.

Table 5. Operational oil outflow estimates, in tonnes based on 86% compliance with MARPOL legal limits

Ship Type Total Oil Consumed Sludge Generation Legal Discharge 86% compliance

for Vessel Type 15 ppm

Bulk Carriers 043,901,183 0,351,210 05.27 049,175

Combination Carriers 001,878,610 0,015,029 00.23 002,104

Container Vessels 029,184,295 0,233,474 03.50 032,690

Dry Cargo Vessels 015,009,051 0,120,073 01.80 016,812

Miscellaneous 014,263,099 0,114,105 01.71 015,976

Offshore Vessels 011,864,184 0,094,913 01.42 013,289

Ferries/Passenger Vessels 022,935,349 0,183,483 02.75 025,690

Reefer Vessels 007,647,164 0,061,177 00.92 008,566

RoRo Vessels 015,300,591 0,122,405 01.84 017,138

Tankers - All cats. 062,135,997 0,497,088 07.46 006,549

Total 224,119,523 1,792,956 26.89 187,990
16 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

83 The CRUCOGSA Research Programme

(CRUCOGSA 1999; T.J. Gunner, pers. comm.) studied emissions of VOCs from loaded tankers through

in situ studies. A total of 2,024 samples from 361

voyages were taken and an estimate of VOC emissions from transport of crude oil was made:

VOC emissions = Loss percent (Mass) per week per

Vessel + 0.01 x TVP (psi) x (average density of HC

Vapour/average density of crude oil)

Where HC - hydrocarbons 

Where TVP - total vapour pressure in psi

Where VOCs - volatile organic compounds

84 The total VOC loss figure for transport of oil

is given as 7.2 million tonnes VOCs per year (based

on Fairplay statistics for 2000). Under section 3.2.3

of this study, it is noted that tankers are not always

fully loaded; therefore, an average loaded figure for

all tankers is given as 85%. Given this and taking

into account the following variables:

The equation: 

Loss percent (Mass) per week per vessel=0.01 *TVP

(psi)*(average density of HC Vapour/average density of crude oil)

Variables for Calculation:

- Average Density of HC Vapour = 0.54 kg/litre

- Average Density of Crude Oil = 0.84 kg/litre

- Average TVP = 14 psi (98% loaded); 6 psi (85%

- loaded)

- Average size of Crude Oil Tanker = 163,335 dwt

- Average voyage length loaded = 1.56 weeks

- Average Number of Voyages per annum = 20

- Total number of Crude Oil Tankers (circa 2002) =

- 1574

The calculation is as follows, given 85% loaded:

Loss percent

= 0.01*6*(0.54/0.84) = 0.038% per week

= 0.038%*1.56 weeks = 0.06% per average voyage

= 0.06%*163,335 dwt = 98 tonnes per vessel per

= voyage

= 98*20 voyages/yr = 1960 tonnes per vessel/yr.

= 1960*1574 crude oil tankers = 3,085,

= 072 tonnes/yr.

Hence, the total discharge into the atmosphere

of VOC from the carriage at sea of crude oil

by tankers, assuming they are 85% loaded, is estimated at 3,085,075 tonnes/yr., or 3,085,000

tonnes/yr.

85 VOCs from loading must also be added to

this number. Furthermore, a certain amount of VOCs

would be produced during crude oil washing (COW).

This, however, would only be displaced on loading

and can be calculated alongside the loading number.

For this estimate it was assumed that approximately

0.1% of the cargo would be emitted as VOCs. Given

the total cargo transported numbers developed in

section 3.2, the following is an estimation of VOCs

emission during loading:

Total cargo loaded to Crude Oil Tankers

(3,712,961,000) x 0.001 = 3,712,961 tonnes

Combining this figure with the transportation figure, the total emission of VOC from tanker operations is:

VOCs from carriage + VOCs from loading = total

VOC emission from tankers

or

3,085,075 tonnes + 3,712,961 tonnes = 6,798,036

tonnes (approx. 6,800,000 tonnes)

86 To establish the volume of this emission that

enters the ocean, it is essential to establish which

fractions within the VOCs would precipitate to the

sea. Pentane contributes approximately 1% of

VOCs, according to recent USA research. As this is

the main component with a boiling point above 0 deg

C (36 deg C), it represents the fraction of VOCs that

could enter seawater. Based on the following calculation: 

6.798 million tonnes x 0.01 = 67,980 tonnes/yr. or

68,000 tonnes/yr. VOCs

Thus, a total of 68,000 tonnes of oil/yr. could

enter the ocean from VOC emissions.

In contrast to this estimate, recent Norwegian

studies based on measurements on several shuttle

tankers have estimated the average density of HC

vapours at 0.002 kg/l (K.O. Skjolsvik. pers. comm.,

July 2003). This is a 270-fold decrease from the

value (0.54 kg/l) used in the above calculations. If

that value is applied as above, the estimate of oil

from VOC emissions from both carriage and loading

losses that could enter the marine environment

becomes:

[11,426 tonnes (from carriage) + 13,752 tonnes

(from loading)] x 0.01= 252 tonnes/yr. or ~ 250

tonnes/yr. 

The difference in the two estimates shows the

large uncertainty around calculating an input figure

for VOCs from tankers. In addition, losses of VOCs

that occur in ports may not impact the sea but rather

the land, depending upon wind directions and velocities. It has been assumed in this study that all losses of VOCs will enter the sea. Hence, given the

uncertainty of the estimation approach and to be

conservative, the initial figure of 68,000 tonnes/yr. is

adopted for this study’s estimates of total inputs.

Clearly, estimation of this input source requires more

consideration.

3.1.6 VOCs from onboard bunkering and engine

operations

87 VOCs are also emitted from engine operations and from the bunkering of all ship types. Due

to lower volatility of marine fuels, the situation is not
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 17

comparable to that described above for tankers.

However, there is no data available to estimate losses and, therefore, no input figure estimated. More

information about this source is required.

3.2 Operational discharges - cargorelated

3.2.1 Introduction

88 In the 1990 report (MEPC 1990), the statistics on oil movements by sea were used as a basis

for the remaining estimates and assumptions.

Furthermore, certain intra-area movements of oil at

sea were estimated. On updating the figures for this

report, the amount of oil moved and the tonnage

type and voyage frequency data did not match up.

In this case, the total amount of oil moved was seen

as an underestimate, owing to the tonnage of the

world fleet. Due to the lack of complete data for

intra-area movements and owing to the potential for

a specific oil cargo to be carried to its destination by

a number of vessels, i.e. transhipped in different

hulls, the total numbers of tankers were used as the

basis of the estimates of oil transportation and subsequent, cargo-related, operational discharge.

89 By way of explanation for this deviation from

the 1990 model, two examples are given below:

.1 A Very Large Crude Carrier (VLCC, e.g.

300,000 dwt) loads a full cargo in the Arabian

Gulf for discharge at Ain Sukhna in the Red Sea

(potentially an intra- area movement). The cargo

is discharged at Ain Sukhna and is pumped up

the Sumed Pipeline to Sidi Kerir for loading onto

four 100,000 dwt (Aframax) tankers for final discharge in southern European ports for onward

pipeline movement to the end refinery. Within

this total movement of 300,000 tons of cargo,

five ships have been used with a combined dwt

capacity of 700,000 dwt but each ship is capable of creating an operational discharge.

.2 40,000 tons of heavy fuel oil is delivered to

Rotterdam storage from Russia on a long haul

Dirty Petroleum Product (DPP) vessel (42,000

dwt). In Rotterdam, the product is cut/blended

with gas-oil and prepared for delivery by bunker

vessels (6,000 dwt) to ocean going vessels as

bunkers. Earlier figures may have only recorded

the fuel oil movement from Russia to Rotterdam

but the onward movement of a greater combined

tonnage by eight smaller bunker vessels (intraarea movement) is not recorded. This further

movement of the blended material (Gas-oil),

which was locally produced by a refinery, will

have an additional operational discharge potential (which is estimated) associated with the

eight bunker vessels. 

90 Although having supplied two possible

examples to account for the different estimates, creating an apparent increase in the total tonnage

moved by sea, greater problems will occur in the

United States with offshore lightering of VLCC’s in

the United States Gulf, Stapleton (New York) and the

Bigstone anchorage (Delaware). The newly-generated numbers will also take into account, to a greater

extent, further examples such as the crude oil movements between Valdez and the West Coast of the

United States, and the subsequent lightering and

onward movements through Panama to the East

Coast.

3.2.2 Tanker construction and legislation

91 This section provides an overview of the

general features of tanker construction and capability to mitigate operational discharges of oil. As stated in the 1990 report (MEPC 1990), oil tankers during normal operations discharge a certain amount of

oil contained in the ballast and tank-washing water

into the sea. The values of oily discharges were

based on tankers having met MARPOL 73/78 construction, equipment and discharge requirements.

92 Under Regulation 13 of MARPOL 73/78,

tankers over 20,000 tons deadweight that carry persistent oils are required to have segregated ballast

tanks (SBT) and/or a crude oil washing system

(COW), depending upon when they were built and

their size. Segregated ballast tanks are tanks that

are completely separated from the oil cargo and fuel

systems and are permanently allocated to the sole

carriage of water ballast. Dedicated clean ballast

tanks are certain cargo tanks that are cleaned and

then dedicated to the carriage of water ballast. It

must also be noted that, although stated as an alternative under Regulation 13, dedicated clean ballast

tanks (CBTs) on crude oil tankers are an obsolete

provision being replaced by SBT requirements.

However, CBT arrangements may still be found on

certain product tankers such that, like SBT, the tank,

pump and piping systems for CBT will be isolated

from the cargo oil and piping system for the specific

voyage when the CBT arrangement is in use.

93 A crude oil washing (COW) system is a cargo

tank cleaning system that uses crude oil as the

washing medium. Crude oil, under high pressure, is

pumped through fixed but potentially programmable

washing machines positioned in a tank so that oil

impingement on the tank bulkheads and internal

structures cleans off oil residues and sludge remaining in the tank after cargo discharge. The measures

are specifically aimed at reducing operational pollution from tankers due to subsequent ballasting and

tank washing. Crude oil washing (COW) of SBT/DH

(segregated ballast tank/double hulled) tankers is

limited by the lack of necessity to wash cargo tanks

for the receipt of departure ballast. COW can be limited to 25% of the tanks for sludge control only. 

94 For a COW system’s efficiency to be certified

under MARPOL, the extent of the total volume of oil

found floating on top of the total volume of departure

ballast after a COW operation within the cargo tanks

can not exceed 0.00085 of the total volume of each

tank containing the ballast water that has been in
18 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

contact with oil cargo residues. In practice, this very

small volume of oil will never be discharged overboard as it will adhere to the tanker structures during

a ballast decant and will be stripped to the vessel’s

slop tank for further treatment and decanting.

95 Regulation 15 of MARPOL 73/78 requires

that all tankers have slop tanks (3% of their carrying

capacity) in order to undertake load-on-top (LOT)

procedures for recovered oil residues, and an oil discharge monitoring and control system (ODME) to

monitor the amount of oily water from the cargo system that may be discharged to the sea. Regulation 9

of MARPOL 73/78 limits the quantity that may be

discharged at 1/30,000 of the total carrying capacity

for new tankers, and to 1/15,000 for existing tankers.

In addition, this regulation also limits the engine

room oily water discharge concentration to 15 ppm,

which is monitored by the Engine Room 15 ppm

alarm system. Regulation 9 ensures the limitation of

oily water discharges to within permissible limits.

Excess oil residues from the cargo are stored in the

vessel’s slop tanks, where the next crude oil cargoes

may then be loaded on top (LOT) of these remaining

oily residues in slop tanks. 

96 MEPC (1990) found a lack of adequate

reception facilities worldwide to handle the necessary tanker capacity. This situation has not changed

(circa 2001). However, approximately 64% of the

tanker fleet now operates with segregated ballast

tanks, which obviates the need to dispose of ballast.

An amount of tank washing may still need to be disposed of, in compliance with MARPOL. This will

continue to pose serious problems for tankers on

short haul voyages and for vessels operating within

designated “Special Areas” (such as the Black Sea

or Mediterranean Sea, see IMO 1997a, 2002). 

3.2.3 Tanker fleet size

97 Due to MARPOL 73/78, various pollution

prevention requirements apply to varying sizes and

types of vessels, hence the quantity of oil discharged

annually from the various types of ships will differ.

The data are, therefore, arranged within the following

categories in order to take into account the various

regulations and also the current standard size categories used in the tanker market:

.1 Less than 10,000 dwt

.2 10 - 20,000 dwt

.3 20 - 40,000 dwt

.4 40 - 70,000 dwt

.5 70 - 110,000 dwt, e.g. Aframax/Shuttle/lightering tanker

.6 110 – 175,000 dwt, e.g. Suezmax tanker

.7 Greater than 175,000 dwt, e.g. VLCC (Very

Large Crude Carrier)

Data from the Fairplay Database (Fairplay

Database 2000) were used to produce numbers for

tanker type and tonnage distribution greater than

5,000 dwt, up to the year 2000, for delivery/delivered

tonnage (Table 6).

Table 6.

Tanker types and tonnage distribution (circa 2000)

Size Category Number of Tonnage

Vessels (dwt)

1 Less than 10,000 dwt 0,285 002,029,347

2 10 - 20,000 dwt 0,344 005,300,048

3 20 - 40,000 dwt 0,683 021,540,848

4 40 - 70,000 dwt 0,609 031,630,838

5 70 - 110,000 dwt 0,618 057,069,211

6 110 - 175,000 dwt 0,366 054,465,230

7 Greater than 175,000 dwt 0,516 149,087,730

Total 3,421 321,123,252

98 The average Annex I (MARPOL 73/78) tanker

tonnage is 93,868 dwt, with the average crude oil

tanker tonnage being 163,335 dwt. The vessel size

categories and numbers from the Fairplay database,

as shown, are carried forward and used together

with further estimates in the section below, which

focuses on further subdivision of the tanker types

with the estimates on voyage frequencies.

3.2.4 Assumptions to the outflow model 

99 In order to comply with MARPOL 73/78

requirements, 60% (25% for sludge control, combined with sufficient washing for departure ballast) of

a vessel’s cargo tanks for pre-MARPOL tankers (single hull/non-SBT), and 25% for the MARPOL

(SBT/DH) crude oil carriers may be crude oil washed

(COWed). Some tanker terminals only require a minimum COW to be performed, i.e. 25% sludge control

for SBT vessels. 

100Industry sources provided a practical viewpoint to couple with the regulatory limits. The frequency that vessels washed their tanks with water

was obtained. The estimates of oil inputs were

derived, as shown below, and are believed to be a

fair indication of industry practice.

3.2.4.1 Crude oil tankers 

101 MARPOL (double hull/separated ballast

tank (SBT)) tankers: These tankers do not, as a matter of course, have to wash their cargo tanks with

water during the ballast voyage. However, an industry estimate is that they water wash 3 to 4 cargo

tanks, twice a year, for in-tank inspection purposes.

For this purpose, they use about 3,000 m3 of water

which is discharged with an oil content not more

than 15 ppm. Thus, per annum, a tanker of this type

discharges 6,000 m3 of water containing 15 ppm of

oil, or a discharge of 90 litres of oil for an oil-transported quantity of approximately 2,400,000,000

litres. Thus, approximately 100 litres oil is discharged; this oil outflow factor would be

1/24,000,000, or 0.04 x10-6.

102 Pre-MARPOL (hydrostatic balance loading (HBL)) tankers: In an operator’s study

(Intertanko, unpubl.), an evaluation of the extent of
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 19

oil discharge for the ships of this type derived a value

of 350 litres per voyage for a 300,000 m3 cargo. As

these vessels undertake 8 voyages per annum (see

voyage frequency figures, Section 3.2.6), the total oil

outflow is 2,800 litres or 2.8 m3 against a total cargo

carried of 2,400,000 m3. Thus, the total outflow for

one ship is approximately 3.0 m3, a factor of

1/800,000, or 1.25 x 10-6.

103 The average size of a crude oil tanker as

calculated from the figures quoted in this model is

163,333 tonnes dwt. Assuming such a vessel discharges 30% of her deadweight as arrival ballast

water with an oil content of 15 ppm (worst-case scenario), the tonnage of ballast water discharged would

be 49,000 tonnes with an oil content of 735 litres.

Thus, the oil outflow factor is 1/222,222, rounded to

1/223,000, or 4.5 x 10-6; this takes into consideration

a proportion of the ballast tonnage discharged as

being segregated ballast which is not contained in

designated crude oil cargo tanks as clean arrival ballast. Compared with the foregoing operator’s study,

this derived oil outflow factor supplies a worst-case

scenario. 

3.2.4.2 Product and chemical tankers

104 Although the prime categories for product tankers are shown falling into two types, namely

Clean Petroleum Products (CPP) and Dirty Petroleum

Products (DPP), the hull design affecting the operation of the vessel is taken into account within the

final calculations to determine the extent of operational pollution from these types of vessels. The categories of SBT (not having ballast in cargo tanks)

and the single hull product vessels, therefore, which

need to practice Load on Top (LOT), have created a

secondary division of category for the purposes of

this study.

105 Clean Petroleum Product (CPP): A CPP

vessel has between 16 and 20 cargo tanks with 2

slop tanks. It is estimated that the cargo tanks contain about 100 litres oil after discharge, giving a total

cargo content remaining onboard of roughly 2 m3

.

The cargo tanks are washed after discharge in readiness for the next cargo and the washings are

returned to one of the slop tanks for primary settling.

This type of cargo is light (density wise) and will

readily separate from its associated wash water. The

wash water is then decanted to the second slop tank

for further separation and then discharged (from the

bottom) over the side via the oil discharge monitor

(ODME). On these ships, the inherent problems of

the ODME operation are not as common as with DPP

cargoes, as the optical systems do not get obstructed with black sludge, and, therefore, they tend to

operate more efficiently. After decanting the majority of the wash water in the slop tanks, the balance of

the oily water residue is discharged to lighters or

slop facilities. This can be accepted, given that the

loading of CPP will take place normally at a refinery

where such slops can be easily treated alongside

refinery water (wash water, etc.). This will result in a

zero discharge by CPP tankers to the sea but in the

most improbable and worst-case scenario - a maximum of 2 m3 oil per voyage from 45,000 dwt, or a

factor of 1/22,500 for non-conformity. This oil outflow factor lies between the two required factors and

would allow compliance for older vessels. (Note:

MARPOL 73/78 requirements, Regulation 9, also

allow a maximum instantaneous outflow of 30 litres

of oil content per nautical mile; thus, 2 m3 can be discharged over a distance of 67 or approximately 70

nautical miles, outside of designated special areas). 

106 Dirty Petroleum Product (DPP):

Estimates of the amount of cargo remaining in the

tanks after discharge have been around 300 litres per

tank, with ships having between 16 and 20 tanks.

Thus the maximum discharge would be 6 m3from a

total cargo of about 42,000 m3- i.e. 1/7000 or

0.014% of cargo. This is in excess of the Regulation

9 limits of 1/15,000 ratio (the maximum allowed for

these types of vessels together with their age). In

the example used, the operator estimated an average of 450 m3 slop tank size on these ships. If 450

m3 is, therefore, discharged with an oil content of 15

ppm (similar to the engine room outflow criteria for

similar oils), then the quantity would be roughly 67.5

litres discharged with the wash water – rounded up

to 100 litres of oil. Thus, 100 litres from a cargo of

42,000 m3 would give a factor of 1/420,000. This has

been rounded down to 1/400,000 or 2.5 x 10-6, owing

to the initial rounding up to 100 litres.

107 On the above basis, the following operational outflow factors were:

Operational Outflow Factors:

Crude Oil (Double Hull/SBT) 4x10-8 

Crude Oil (Pre MARPOL/HBL) 4.5x10-6

Products (Double Hull/SBT (CPP & DPP)) Negligible

Products (Single Hull (CPP & DPP)) 2.5x10-6

Chemical Treated as per Product tankers

108 The outflow factors were derived from

estimates gained from a number of industry operators. The guiding factor in these estimates was the

limit on the Oil Discharge Monitor (ODME) before it

operates a shut down or valve closure. This limit is

now 15 ppm (Regulations 9 and 16), except in MARPOL Special Areas where the limit is zero. It must be

noted that 15 ppm oil in water is the maximum legal

discharge limit and that a number of vessels will

operate at levels well within this concentration. For

this study, the worst-case scenario of 15 ppm is

used.

3.2.5 Distinction between short haul and long

haul voyages

109 Based on estimates from the industry

(tanker operators and individual experts), the following distinctions were made for short haul and long

haul voyages for the main three tanker types. The

definitions of short haul and long haul voyages are

consistent with MEPC (1990), i.e. a tanker on a short

haul voyage is considered to be:
20 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

.1 on a voyage of less than 72 hours or 1,200

nautical miles;

.2 operating within a Special Area under

Regulation 10 of MARPOL 73/78;

.3 operating under a specific trade exemption

under regulation 13C of MARPOL 73/78; or

.4 carrying asphalt or other products which

have physical properties that inhibit effective

oil/water separation and monitoring.

110 Chemical/oil tankers have been corrected for the period of time when these vessels are carrying Annex 1 cargoes. Thus, factors of between

0.175 (17.5%) and 0.3 (30%) have been applied to

the tonnage divisions for short haul and long haul

voyages, respectively.

111 The distribution of tonnage for short haul

and long haul voyages for the Product and

Chemical/Oil tankers relies upon the following standard divisions:

Less than 10,000 dwt 100% Short Haul

10 - 20,000 dwt 50 / 50 Short/Long Haul

20 - 40,000 dwt 30 / 70 Short/Long Haul

40 –70,000 dwtq 10 / 90 Short/Long Haul

Greater than 70,000 dwt 100% Long Haul

112 The distribution of tonnage for long and

short haul voyages for Crude Oil tankers relies upon

the following standard divisions:

Less than 40,000 dwt 100% Short Haul

40 –70,000 dwt 50 / 50 Short/Long Haul

70 – 110,000 dwt 20 / 80 Short/Long Haul

110 – 175,000 dwt 15 / 85 Short/Long Haul

Above 175,000 dwt 100% Long Haul

113 For each tanker type category, data

from the Fairplay Database (2000)

(www.fairplay.co.uk/databases) were used to produce the tonnage figures in Tables 7 to 9.

Table 7.

Tonnage distributions, in tons dwt, of chemical/

oil tankers for long- and short-haul voyages,

after correction for proportions used in Annex I

cargoes

Ship size, dwt Long Haul Short Haul

LT 10,000 0 159,491

10 – 20,000 166,721 166,721

20 – 40,000 240,138 102,917

40 – 70,000 772,250 085,805

70 – 110,000 0 0

110 – 175,000 0 0

GT 175,000 0 0

Total 1,179,109 514,934

Table 8. Tonnage distributions, in tons dwt, of product tankers for long- and short-haul voyages

Ship size, dwt Long Haul Short Haul

DPP1 CPP2 DPP CPP

LT 10,000 0 0 468,355 763,539

10 – 20,000 895,609 740,790 895,609 740,790

20 – 40,000 9,019,500 4,165,508 3,865,502 1,785,218

40 – 70,000 7,757,123 10,479,614 831,662 1,143,044

70 – 110,000 1,253,586 5,841,945 0 0

110 – 175,000 2,040,701 2,942,262 0 0

GT 175,000 880,336 0 0 0

Total 21,846,855 24,170,119 6,061,128 4,432,591

1 DPP – dirty petroleum product 2 CPP – clean petroleum product

Table 9. Tonnage distributions, in tons dwt, of crude tankers for long- and short-haul voyages

Ship size, dwt Long Haul Short Haul

Double Single Double Single

Lt 10,000 0 0 0 0

10-20,000 0 0 65,830 56,042

20-40,000 0 0 97,086 647,722

40-70,000 1,316,731 2,962,876 1,316,730 2,962,875

70-110,000 15,000,000 24,256,560 9,717,120 1,000,000

110-175,000 17,253,082 24,681,065 7,548,120 0

Gt 175,000 49,190,415 99,016,975 0 0

Total 82,760,228 150,917,476 18,744,886 4,666,639

(Note: Single - means that vessel is not registered as having a double form (hull, bottom or sides) of construction. This does not mean that the vessel is not operating with SBT. Double - means that the vessel is registered either with a double hull, double bottom or double sides. Thus, the vessel will probably have sufficient double hull capacity for ballast.)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 21

3.2.6 Voyage frequency

114 Voyage factors for each size category of

vessel were estimated using information taken from

the shipping industry. These were estimated based

on the size of the respective vessel categories and

the description as supplied above for the definition

of a short voyage. The following numbers of voyages per annum have been used in the matrix below

and in Table 10:

Lt 10,000 dwt 40 voyages per annum

10-20,000 dwt 40 voyages per annum

20-40,000 dwt 32.5 voyages per annum

40-70,000 dwt 30 voyages per annum

70-110,000 dwt 30 voyages per annum –

e.g. Aframax/Shuttle/lightering

tanker

110-175,000 dwt 15 voyages per annum –

e.g. Suezmax tanker

Gt 175,000 dwt 8 voyages per annum –

e.g. VLCC

115 Values in Table 10 have been multiplied

with the tonnage figures given earlier for the respective tanker types and sizes to give the matrix (Table

11) illustrating the total tonnage of oil (Annex 1 cargoes) shipped (100% dwt) by the world’s tanker tonnage (million tonnes).

116 Further consideration was then given to

the sub-categories as explained earlier, i.e. LOT,

SBT and COW tankers. Table 12 subdivides the

above matrix categories onto the defined subcategories. Table 12 shows the total oil shipped by the

world’s tanker fleet, assuming 100% dwt capacity is

used.

117 Using data from the CRUCOGSA database and estimates from industry sources, it is

assumed that

.1 70% of all tankers carry a full cargo – average 98% loaded;

.2 30% of all tankers are partially loaded, at

60% (this percentage includes an allowance

for product part cargoes);

.3 the average correction applicable given .1

and .2 above is, therefore, 0.845 (84.5%).

118 Using the foregoing matrix of total oil

cargo tonnage carried, the final oil outflow matrix

(Table 14) was developed, using the outflow factors

developed in Paragraph 3.2.4 above, assuming

100% compliance with MARPOL 73/78.

119 In developing the final figure of 5728

tonnes or ~5700 tonnes of oily waste discharge from

Table 10. Matrix of voyage frequency (laden voyages per annum) for vessel type and size

Dwt Size Crude Oil Products Chemical/Oil

Long Haul Short Haul Long Haul Short Haul

Double Single Double Single DPP CPP DPP CPP Long Haul Short Haul

Lt 10,000 40 40 40 40 40 40 40 40 40 40

10-20,000 40 40 40 40 40 40 40 40 40 40

20-40,000 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5 32.5

40-70,000 30 30 30 30 30 30 30 30 30 30

70-110,000 30 30 30 30 30 30 30 30 30 30

110-175,000 15 15 15 15 15 15 15 15 15 15

Gt 175,000 8 8 8 8 8 8 8 8 8 8

Table 11. Total tonnage of oil (Annex 1 cargoes) shipped by the world’s tanker fleet (100% dwt, in million tons)

Dwt Size Crude Oil Products Chemical/Oil

Long Haul Short Haul Long Haul Short Haul

Double Single Double Single DPP CPP DPP CPP Long Haul Short Haul

Lt 10,000 0 0 0 0 0 0 18.734 30.542 0 6.380

10-20,000 0 0 2.633 2.242 35.824 29.632 35.824 29.632 6.669 6.669

20-40,000 0 0 3.155 21.051 293.134 135.379 125.629 58.020 7.804 3.345

40-70,000 39.502 88.886 39.502 88.886 232.714 314.388 24.950 34.291 23.167 2.574

70-110,000 450.000 727.697 291.514 30.000 37.608 175.258 0 0 0 0

110-175,000 258.796 370.216 113.222 0 30.611 44.134 0 0 0 0

Gt 175,000 393.523 792.136 0 0 7.043 0 0 0 0 0

Totals 1,141.81 1,978.95 450.026 142.179 636.934 698.791 205.137 152.485 37.640 18.968

Grand Total 3,712.961 1,749.955
22 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Table 12. Outflow matrix for calculations of oily waste discharge from tanker cargo operations assuming 100%

loading

Dwt Size Crude Oil Products Chemical/Oil

Long Haul Short Haul Long Haul Short Haul CPP - See (2)

Double Single Double Single DPP CPP DPP CPP Long Haul Short Haul

0 0 0 0 0 0 18.734 30.542 0 6.380

With SBT 0 0 0 0 0 0 2.955 10.780 0 2.730

With LOT 0 0 0 0 0 0 15.779 19.762 0 3.650

10– 20000 0 0 2.633 2.242 35.824 29.632 35.824 29.632 6.669 6.669

With SBT 0 0 2.633 1.975 12.330 26.840 12.330 26.840 4.720 4.720

With LOT 0 0 0 0.267 23.494 2.792 23.494 2.792 1.949 1.949

20- 40000 0 0 3.155 21.051 293.134 135.379 125.629 58.020 7.804 3.345

With SBT 0 0 3.155 14.780 45.980 43.940 19.705 18.830 4.945 2.120

With LOT 0 0 0 6.271 247.154 91.349 105.924 39.190 2.859 1.225

40-70000 39.502 88.886 39.502 88.886 232.714 314.388 24.950 34.291 23.167 2.574

With SBT 39.502 67.005 39.502 67.005 61.645 162.700 6.610 17.745 19.160 2.130

With

COW/LOT 0 21.881 0 21.881 171.069 151.688 18.340 16.546 4.007 0.444

70-110000 450.000 727.697 291.514 30.000 37.608 175.258 0 0 0 0

With SBT 450.000 424.180 291.514 17.490 4.795 130.470 0 0 0 0

With COW 0 303.517 0 12.510 32.813 44.788 0 0 0 0

110-175000 258.796 370.216 113.222 0 30.611 44.134 0 0 0 0

With SBT 258.796 182.000 113.222 0 0 41.415 0 0 0 0

With COW 0 188.216 0 0 30.611 2.719 0 0 0 0

393.523 792.136 0 0 7.043 0 0 0 0 0

With SBT 393.523 427.815 0 0 0 0 0 0 0 0

With COW 0 364.321 0 0 7.043 0 0 0 0 0

Totals 1,141.821 1,978.935 450.026 142.179 636.933 698.791 205.137 152.484 37.641 18.967

Grand Total SBT = 3,480.532 LOT/COW = 1,982.382

(Note: All Crude Oil tankers built before 1975 have been retrofitted for SBT. All Crude/Oil tankers built between 1975 and 1980 are still operating with COW. All Crude

Oil tankers with a Double Bottom, Double side or Double Hull have sufficient ballast space to be classified as SBT. All Chemical/Oil Tankers are operating with CPP

only.)

Table 13. Outflow matrix for calculations of oily waste discharge from tanker cargo operations assuming 100%

loading

Dwt Size Crude Oil Products Chemical/Oil

Double Single Double Single DPP CPP DPP CPP Long Haul Short Haul

0 0 0 0 0 0 15.830 25.808 0 5.391

With SBT 0 0 0 0 0 0 2.497 9.109 0 2.307

With LOT 0 0 0 0 0 0 13.333 16.699 0 3.084

10– 20000 0 0 2.225 1.894 30.272 25.039 30.272 25.039 5.635 5.635

With SBT 0 0 2.225 1.669 10.419 22.680 10.419 22.680 3.988 3.988

With LOT 0 0 0 0.225 19.853 2.359 19.853 2.359 1.647 1.647

20-40000 0 0 2.666 17.788 247.698 114.395 106.156 49.027 6.595 2.826

With SBT 0 0 2.666 12.489 38.853 37.129 16.651 15.911 4.179 1.791

With LOT 0 0 0 5.299 208.845 77.266 89.506 33.115 2.416 1.035

40-70000 33.379 75.109 33.379 75.109 196.643 265.658 21.083 28.976 19.577 2.175

With SBT 33.379 56.619 33.379 56.619 52.090 137.482 5.585 14.995 16.190 1.800

With

COW/LOT 0 18.490 0 18.490 144.553 128.177 15.497 13.982 3.386 0.375

70-110000 380.250 614.904 246.329 25.350 31.778 148.093 0 0 0 0

With SBT 380.250 358.432 246.329 14.779 4.052 110.247 0 0 0 0

With COW 0 256.466 0 10.571 27.726 37.846 0 0 0 0

110-175000 218.683 312.832 95.672 0 25.866 37.293 0 0 0 0

With SBT 218.683 153.790 95.672 0 0 34.996 0 0 0 0

With COW 0 159.042 0 0 25.866 2.297 0 0 0 0

332.527 669.355 0 0 5.951 0 0 0 0 0

With SBT 332.527 361.504 0 0 0 0 0 0 0 0

With COW 0 307.850 0 0 5.953 0 0 0 0 0

Totals 964.839 1,672.200 380.272 120.141 538.208 590.479 173.341 128.849 31.806 16.027

Grand Total SBT = 2,941/05 LOT/COW = 1,675,113
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 23

tanker cargo operations, the following assumptions

were used in the final oil outflow matrix (Table 14):

.1 All Annex 1 tankers comply with MARPOL

Regulations – 94% of States are Parties to

MARPOL 73/78 – All Charterers require compliance as a specific term in every Charter Party.

.2 Operational Outflow Factors (as explained in

section 3.2.4.2):

Crude Oil (Double Hull/SBT) 4 x 10-8

Crude Oil (Pre MARPOL/HBL) 4.5 x 10-6

Products (Double Hull/SBT

(CPP & DPP)) ZERO

Products (Single Hull

(CPP & DPP)) 2.5x10-6

Chemical Treated as per product tankers

120 In section 3.1, it was stated that, based

on IMO figures for PSC (IMO, FSI 9/8, 2001) detentions, an average of 86% compliance was used. In

order to estimate the actual outflow, this compliance

figure was used, coupled with an estimate of

1/50,000 discharge as a non-compliant, outflow factor.

3.2.7 Summary of operational discharges – cargorelated

121 Based on the above calculations,

the estimated discharge of oil into the marine

environment from cargo-related, tanker

activities, which includes tank washing and oil in

ballast, is 19, 250 tonnes/yr, or ~19,000

tonnes/yr.

Table 14. The final oil outflow matrix for calculations of oil discharge from tanker cargo operations, in tonnes

Dwt Size Crude Oil Products Chemical/Oil

Long Haul Short Haul Long Haul Short Haul

Double Single Double Single DPP CPP DPP CPP Long Haul Short Haul

0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With LOT 0 0 0 0 0 0 33.334 41.746 0 7.710

10– 20000 0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With LOT 0 0 0 1.011 49.632 5.897 49.632 5.897 4.117 4.117

20- 40000 0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With LOT 0 0 0 23.762 522.112 193.165 223.764 82.788 6.041 2.587

40-70000 0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With

COW/LOT 0 82.913 0 82.913 361.383 320.442 38.743 34.954 8.466 0.938

70-110000 0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With COW 0 1,150.097 0 47.403 69.317 94.615 0 0 0 0

110-175000 0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With COW 0 713.195 0 0 64.665 5.744 0 0 0 0

0 0 0 0 0 0 0 0 0 0

With SBT 0 0 0 0 0 0 0 0 0 0

With COW 0 1,380.498 0 0 14.878 0 0 0 0 0

Totals 0 3,326.704 0 155.089 1,081.986 619.863 345.472 165.386 18.623 15.352

Grand Total SBT = 0 LOT/COW = 5,728.476 tonnes

Table 15. Summary matrix of operational discharges – cargo-related (values in tonnes/yr.)

Crude Oil Products Chemical Totals

/Oil

LH SH LH SH

Dwt DH SgH DH SgH DPP CPP DPP CPP LH SH

Totals 964.839 1,672,200 380.272 120.141 538.208 590.479 173.341 128.849 31.806 16.027 461,616.268

86% Com 829.762 1,438.092 327.034 103.321 462.859 507.812 149.073 110.810 27.354 13.784 39,698.999

Non Com 135.077 234.108 53.238 16.820 75.349 82.667 24.268 18.039 4.453 2.244 646,262.775

Out Flow 0.000 11,131.003 0.000 799.720 2,664.130 2,922.869 858.038 637.803 157.442 79.336 19,250.340
24 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

3.3 Accidental discharges of oil

122 This section first considers accidental

inputs from all sea-based activity sources and then

focuses exclusively on ships (tankers, other vessels

or non-tankers).

3.3.1 Accidental spillage from all sea-based

activity sources15

123 The recorded annual numbers of accidental oil spills into the marine environment of at

least 34 tonnes that occurred during 1968-1999

from all point sources, including vessels, pipelines,

offshore exploration and production activities, shoreline facilities, and unknown sources, are shown in

Table 16. The annual amounts spilled are shown in

Table 17. Total numbers of spills and amounts

spilled annually are shown graphically in Figure 7.

War-related incidents are separated out from accidental spills in Figure 8. The relatively enormous

amount of oil spillage associated with the 1991 Gulf

War is also illustrated here.

124 After rising in the first decade between

1968 and 1977, spill numbers have dropped and levelled off in the following 15 years. Part of the apparent initial increase in spillage may in part be due to

reduced spill reporting during the earlier time period.

In the same three decades, the amount spilled

Table 16. Annual number of accidental, sea-based oil spills of 34 tonnes and over (based on ERC database)

Year Tankers Tankers Barges Non- Pipelines Pipelines E&P E&P Facilities Facilities Unknown/

Military Tankers Military Military Military Other TOTAL

1968 15 0 0 0 0 0 0 0 15

1969 13 0 0 0 0 0 0 0 13

1970 17 0 1 1 1 0 0 0 20

1971 10 0 0 1 0 1 0 0 12

1972 19 0 0 1 0 0 0 0 20

1973 21 0 0 3 1 1 2 1 29

1974 46 0 0 0 0 1 2 0 49

1975 38 0 3 3 0 0 0 0 44

1976 37 0 4 2 0 0 0 0 43

1977 37 0 0 1 0 1 4 0 43

1978 44 0 6 8 1 2 13 0 74

1979 66 0 3 16 1 7 16 2 111

1980 38 0 1 15 0 7 4 3 68

1981 30 0 2 20 0 0 9 1 62

1982 28 1 3 21 7 4 4 0 68

1983 31 0 2 25 2 10 5 0 75

1984 22 2 4 15 1 2 3 0 49

1985 30 3 5 5 2 3 2 0 50

1986 22 29 4 8 4 6 18 1 92

1987 23 24 0 16 3 6 5 0 77

1988 18 1 0 11 2 6 11 1 50

1989 42 1 2 13 0 3 7 0 68

1990 26 1 4 14 0 4 4 3 56

1991 18 8 1 16 4 1 2 1 5 10 1 67

1992 19 3 18 0 1 2 4 47

1993 27 3 15 2 1 3 1 52

1994 27 1 21 1 0 3 4 57

1995 21 0 22 3 1 0 4 51

1996 18 1 20 0 0 3 0 42

1997 22 4 19 4 4 1 2 56

1998 17 3 23 14 3 7 2 69

1999 11 4 10 5 0 7 2 39

Total 853 70 64 363 58 1 76 1 140 10 32 1,668

(Note: Blanks denote no data; 0’s denote no spillages.)

15 This section does not include leisure craft, which are treated

in a separate section and for which only very approximate

estimates are derived.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 25

Table 17. Annual oil spillage, in tonnes, from spills of 34 tonnes and over (based on ERC database)

Year Tankers Tankers Barges Non- Pipelines Pipelines E&P E&P Facilities Facilities Unknown/

Military Tankers Military Military Military Other TOTAL

1968 156,497 0 0 0 0 0 0 156,497

1969 142,272 0 0 0 0 0 0 142,272

1970 219,675 1,129 85 14,286 0 0 0 235,175

1971 203,786 0 520 0 14,286 0 0 218,592

1972 253,417 0 88 0 0 0 0 253,505

1973 86,901 0 255 952 0 0 0 88,108

1974 208,888 0 0 0 150 40,008 34 249,080

1975 263,134 3,119 2,000 0 0 0 0 268,253

1976 331,895 4,187 218 0 0 0 0 336,300

1977 281,211 350 0 0 28,912 315 0 310,788

1978 484,248 0 1,969 34 3,432 79,915 0 569,598

1979 697,959 11,551 2,863 116 477,807 25,437 68 1,215,801

1980 261,213 143 2,732 4,401 44,184 11,259 5,643 329,575

1981 63,142 252 6,704 0 0 106,847 588 177,533

1982 47,523 340 1,047 7,810 6,983 3,007 1,779 0 68,489

1983 437,139 224 4,218 265 280,599 12,097 0 734,542

1984 27,017 8,507 721 8,507 357 1,180 752 0 47,041

1985 101,069 13,606 2,306 2,310 1,622 578 85 0 121,576

1986 28,118 19,388 898 4,024 3,099 38,092 46,133 170 139,922

1987 33,334 23,980 0 3,136 629 8,969 578 0 70,626

1988 207,114 680 0 1,729 310 2,054 2,918 34 214,839

1989 153,431 1,429 2,932 2,939 0 180 619 0 161,530

1990 51,311 255 432 4,757 51 626 1,348 374 59,154

1991 218,440 608,565 2,000 4,315 1,374 83,897 136 14,286 2,160 9,814,020 88 10,749,281

1992 146,683 867 2,454 10,085 827 204 306 161,426

1993 139,153 1,518 3,269 8,262 61 2,493 34 154,790

1994 125,884 129 6,220 157 0 3,848 165 136,403

1995 16,218 0 4,358 384 500 0 187 21,647

1996 81,172 323 7,358 0 0 4,973 0 93,826

1997 74,675 7,262 3,344 1,980 885 34 163 88,343

1998 13,405 13,344 3,839 13,853 440 1,536 782 47,199

1999 22,783 180 2,976 3,902 0 7,083 234 37,158

Total 5,578,707 676,750 54,914 94,997 73,102 83,897 906,905 14,286 352,421 9,814,020 8,870 17,658,869

Figure 7.

Total Non-Military-Related Oil Spills From All

Sources (Spills of at Least 34 Tonnes) (Based on

Environmental Research Consulting Database)

Figure 8.

Total Oil Spillage From All Sources (Spills of 34

Tonnes and Over) (Based on Environmental

Research Consulting Database)
26 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

dropped, although there were unusually high peaks

in 1979 (associated with the Ixtoc I well blowout, and

three very large tanker spills), and in 1983 (with the

Nowruz well blowout and the Castillo de Bellver

tanker spill, the largest tanker spill to date).

125 Table 18 and Figure 9 give estimates of

source-specific annual spill inputs for the ten-year

periods 1968-1977, 1978-1987, and 1988-1997.

These estimates are based on the small spill, factor

estimation methodology. Vessels consistently constitute the largest source of accidental spillage over

all time periods, except for the large Gulf War-related incidents of 1991. However, the largest exploration and production spills of 1979 and 1983 significantly increased the percentage contribution of

these source types with a corresponding reduction in

the vessel spill amount percentages for these years

and the time periods incorporating these years.

Figures 11 to 13 show the relative percentages of

accidental oil spillage by source type for the three

ten-year time periods.

126 The estimates of oil input into the marine

environment from accidental releases from all

sources during the years 1988-1997, based solely on

ten-year averages, are:

Tankers: 157,900 tonnes/yr.

Non-Tankers: 5,300 tonnes/yr.

Facilities: 2,400 tonnes/yr.

Pipelines: 2,800 tonnes/yr.

Exploration and Production: 600 tonnes/yr.

Other and Unknown Sources: 200 tonnes/yr.

War-related activities: 1,052,200 tonnes/yr.

Total accidental spill input: 169,200 tonnes/yr. or

169,000 tonnes/yr

(without war-related spillage; note, Figs 10-13 do

not include this source)

Total accidental input (including war-related

spillage): 1,221,500 tonnes/yr. or 1,220,000

tonnes/yr.

Table 18. Estimated average annual oil input from ships and other sea-based activities, in tonnes, for three, tenyear time periods (based on ERC database)

Source Time Period

1968-1977 1978-1987 1988-1997

Tankers 281,155 286,558 157,895 

Tankers (Military Incidents) No data 6,650 61,025 

NonTankers 413 5,772 5,312 

Pipelines 1,845 2,120 2,736 

Pipelines (Military Incidents) No data No data 8,390 

E&P 5,248 103,856 638 

E&P (Military Incidents) No data No data 1,429 

Facilities 52,572 37,142 2,425 

Facilities (Military Incidents) No data No data 981,402 

Unknown No data 647 135 

Total Average Non-Military Input 341,233 or 341,000 436,095 or 436,000 171,551 or 172,000 

Total Average Military Input No data 6,650 1,052,246 

Total Input (incl. Military Incidents) 341,233 or 341,000 442,745 or 443,000 1,223,797 or 1,220,000

(Note: Estimates were based on use estimation factors for small spills.)

Figure 9.

Estimated Annual Oil Spill Input For Ten-Year Periods

By Source Type Excluding Military Incidents (Based

on Environmental Research Consulting Database)

Figure 10.

Total Oil Input into Marine Environment By Source

Type 1968-1977 (Based on Environmental Research

Consulting Database)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 27

127 The estimates for average annual oil

input for the last decade are based on data of actual spills recorded, with an adjustment for the

absence of data on spills under 34 tonnes, which

were not recorded in the database used. The small

spill estimation factors have been used to increase

the accuracy of the data, taking into account the lack

of data on small spills of under 34 tonnes. Hence,

there may be unavoidable gaps in records on spills

of over 34 tonnes; this might create underestimates

in accidental spillage figures even after the small spill

estimation factors are applied both to spill number

and spill amount. The estimates for average annual

oil input should, therefore, be viewed in this context

as underestimates. 

128 The same methodology was used to

estimate accidental and war-related spill input from

the previous two ten-year time periods, 1968-1977

and 1978-1987. The estimates are shown in Table

19.

129 When the input estimates from the different source types are further broken down into spills

of less than and more than 5,000 tonnes, the influence of the very large spills on overall amounts is

very clear. Figure 13 shows estimated average annual inputs by source types for 1988-1997 with respect

to spill size. Table 20 gives annual input estimates,

from small and large spills, by source types and spill

size for the three time periods. There were 35

tanker/barge spills of greater than 5,000 tonnes and

two spills of this magnitude from marine pipelines

during 1988-1997. There were no other spills greater

than 5,000 tonnes in any other source category during this time period.

130 The estimates for average annual oil

input into the marine environment, from accidental

releases from all point source types of ships and

shipping activity, for the period of 1988-1997, are:

Tankers:

16,300 tonnes/yr. in <5,000-tonne spills 

plus an average of 144,000 tonnes/yr. in spills

>5,000 tonnes

with an overall average input of 160,300 tonnes/yr.

Non-tankers:

5,300 tonnes/yr. in spills of >5,000 tonnes

Facilities: 2,400 tonnes/yr. in spills of <5,000 tonnes

Pipelines:

900 tonnes/yr. in <5,000-tonne spills 

plus an average of 1,900 tonnes/yr. in spills >5,000

tonnes

with an overall average input of 2,800 tonnes/yr.

Exploration and production: 600 tonnes/yr. in spills

of <5,000 tonnes

Other/unknown sources: 200 tonnes/yr. in spills of

<5,000 tonnes

Total accidental release input:

20,400 tonnes/yr. in spills < 5,000 tonnes

plus 151,200 tonnes/yr. in tankers, non-tankers

and pipeline spills of > 5,000 tonnes for an overall

average spill input from all sources of 171,600

tonnes/yr.

War-related incident input: 1,052,300 tonnes/yr. in

spills of all sizes.

3.3.2 Accidental discharges from ships

3.3.2.1 Accidental discharges from tankers

131 The estimated annual number of oil spills

over 0.003 tonnes (1 US Gal.) and the estimated

amount of oil spilled annually by tankers (including

barges and all types of tank vessels carrying oil as

cargo) are shown in Figure 14. The number of spills

Figure 11.

Total Estimated Oil Spill Input By Source Type 1978-

1988 (Based on Environmental Research Consulting

Database)

Figure 12.

Estimated Total Oil Spillage By Source Type 1988-

1997 (Based on Environmental Research Consulting

Database)
28 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Table 19. Estimated average annual oil input, in tonnes, for three, ten-year time periods – a summary (based on

ERC database)

Source Time Period

1968-1977 1978-1987 1988-1997

Tankers 281,200 286,600 160,300 

Non-Tankers 400 5,800 5,300 

Pipelines 1,800 2,100 2,800 

E&P 5,200 103,900 600 

Facilities 52,600 37,100 2,400 

Unknown No data 600 200 

Total Average Non-Military Input 341,200 436,100 171,600 

Total Average Military Input No data 6,600 1,052,300 or 1,052,000

Total Input (incl. Military Incidents) 341,200 or 341,000 442,700 or 443,000 1,223,900 or 1,224,000

(Note: Estimates are based on use of estimation factors for small spills.)

Table 20. Estimated annual average input, in tonnes, from smaller and large spills by source type (based on ERC

database)

Source 1968-1977 1978-1987 1988-1997

Tankers/Barges

(>5,000-tonne spills) 260,300 258,000 144,000 

Tankers/Barges

(<5,000-tonne spills) 18,600 38,000 16,300

Non-Tankers

(>5,000-tonne spills) 0 0 0

Non-Tankers

(<5,000-tonne spills) 500 600 5,300 

Facilities

(>5,000-tonne spills) 4,600 30,300 0

Facilities

(<5,000-tonne spills) 100 2,700 2,400 

Pipelines

(>5,000-tonne spills) 1,700 700 1,900 

Pipelines

(<5,000-tonne spills) 100 1,300 900 

E&P

(>5,000-tonne spills) 5,600 96,900 0

E&P 

(<5,000-tonne spills) 17 2,600 600 

Unknown

(>5,000-tonne spills) 0 0 0

Unknown

(<5,000-tonne spills) 4 900 200 

Total 291,400 432,200 171,600 

(Note: Estimates are based on small spill estimation factors and rounding.)

Figure 13.

Average Annual Oil Spill Input by Source Type

1988-1997 (Based on Environmental Research

Consulting Database)

Figure 14.

Estimated Annual Oil Spills From Tankers 1968-1999

– Amounts Spilled and Estimated Number of Spills

(Based on Environmental Research Consulting

Database)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 29

and amount spilled both increased during the 1960s,

reaching a peak in 1979, subsequently decreasing

before levelling off in the mid-1980s. Since the mid1990s, there has been an additional drop in spill

numbers. The estimates do not include tanker spills

related to acts of war. The estimates also exclude

recent, important large spills 1999-2002 (e.g. Erika,

off France; Prestige, off Spain). There has also been

better reporting since the 1970s, increasing confidence in any trend analysis as time proceeds. 

132 The amount of oil released into the

marine environment from tanker spills varies considerably from one year to the next and it is highly

dependent on the number of very large spills that

occur, as explained in Section 2.3.5. A list of the

non-war-related tanker spill incidents, each involving

at least 50,000 tonnes, is shown in Table 21. Figure

15 shows the influence of these large spills on overall tanker oil spillage for the years 1968-1999.

133 The estimates for average annual oil

input into the sea from accidental spills from all

tankers, based on 1988-1997 data, are:

Tankers:

16,300 tonnes/yr. in <5,000-tonne spills 

plus an average of 144,000 tonnes/yr. in spills

>5,000 tonnes

with an overall average input of 160,300 tonnes/yr.

or ~160,000 tonnes/yr.

3.3.2.2. Accidental discharges from non-tankers

134 The estimated annual number of oil spills

over 0.003 tonnes (1 US gal.) and the estimated

amount of oil spilled annually by non-tankers (all

other vessels carrying oil as fuel, but not cargo,

including, but not limited to cargo vessels, bulk carriers, passenger vessels, and fishing vessels) are

shown in Figure 16. The number of spills as well as

the amount spilled rose dramatically in the late

1970s. This apparent increase of spillages from

these vessels is most likely due to the increased

reporting and recording of data on these incidents.

135 The variability of spill amounts from nontankers from year to year is similar to that of tankers.

However, the overall amounts of oil spilled are about

Table 21. Worldwide Tanker Spills since 1960, Over 50,000 Tonnes1. Recent, well-publicized, European spills

such as Erika (1999) and Prestige (2002) are not shown, nor is the well-known Exxon Valdez spill which was only

37-38,000 tonnes.

YEAR TANKER NAME LOCATION TONNES SPILLED (as reported)

1983 Castillo de Bellver South Africa 267,007

1978 Amoco Cadiz France 233,565

1988 Odyssey North Atlantic Canada 146,599

1979 Atlantic Empress2 Trinidad and Tobago 145,252

1991 Haven Italy 144,000

1979 Atlantic Empress2 Barbados 141,102

1967 Torrey Canyon United Kingdom 129,857

1972 Sea Star Oman 128,891

1980 Irenes Serenade Greece 124,490

1971 Texaco Denmark Belgium 107,143

1979 Independentza Turkey 98,255

1969 Julius Schindler Portugal 96,429

1976 Urquiola Spain 95,714

1993 Braer United Kingdom 85,034

1975 Jakob Maersk Portugal 82,503

1992 Aegean Sea Spain 74,490

1985 Nova Iran 72,626

1996 Sea Empress United Kingdom 72,361

1989 Khark 5 Morocco 70,068

1971 Wafra South Africa 68,571

1960 Sinclair Petrolore Brazil 60,000

1983 Assimi Oman 53,741

1974 Yuyo Maru No. 10 Japan 53,571

1991 ABT Summer Angola 51,020

1992 Katina P. South Africa 51,020

1965 Heimvard Japan 50,000

1 Not including military-related tanker incidents.

2 The Atlantic Empress was involved in a collision which resulted in a spill in Trinidad and Tobago and then broke up while under tow resulting in another spill nearly two weeks later nearly 1,000 km from the location of the first spill. Some records report these two incidents as one spill involving 286,354

tonnes, making it the largest recorded tanker spill. The incidents are reported separately here due to the time period between the two incidents and the

fact that the two spills occurred in different locations creating oil inputs and environmental impacts in different locations. For records maintained on the

histories of individual vessels, these incidents may more logically be considered as a single incident.
30 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

two orders of magnitude smaller from non-tankers

since they carry much less oil (fuel rather than

cargo). Reduced reporting of non-tanker incidents

and incomplete records may also be involved to

some extent since non-tankers have been subject to

less regulation than tankers.

136 The estimated of average annual oil

input from non-tankers is 5,300 tonnes/yr. Since all

spills were less than 5,000 tonnes, no separation for

amounts spilled from larger incidents has been conducted.

3.3.3 Accidental spillage in relation to sea-borne

oil trade

137 In an analysis based largely on Etkin

(1999d), the accidental tanker oil spill data in the

IOSD (with modifications based on ERC data) were

specified with regard to changes in oil transport over

the years 1968-1997. The data were adjusted with

small spill estimation factors using methods

described in Section 2.3.5 and by Etkin (pers.

comm.). Estimation factors derived from a smaller

set of United States Coast Guard spill data were

used to adjust for spills of 0.17 to 34 tonnes. This

analysis was performed to shed more light on the

significance of apparent overall reductions in spillage

despite the fact that, concurrently, there has been

more oil transport in recent years. Presumably, more

oil transport activity would lead to more opportunities for accidental spills from tankers.

138 Figure 17 shows oil movement by

tankers since 1974, according to data from British

Petroleum (BP), 1997. Petroleum tanker transport on

a worldwide basis dipped in the 1980s and rose

again in the 1990s. Inter-area tanker movements for

1997 are also shown in Table 22 and in the map in

Figure 18. Tanker movement is much dependent

upon world events; for example, the oil embargo during the 1990s and the 2003 war in Iraq greatly

reduced tanker movement from that country through

the Persian Gulf and beyond (also see section 3.2.1).

It should also be noted that BP’s estimate of crude

oil transported in the different areas in 1997 (Table

22, totalling ~1,980 million tonnes) is lower than the

Lloyd’s Register, Fairplay Database estimate of oil

transported in 2000 (Table 11, ~3,713 million tonnes),

the latter used to make estimates of operational discharges from tankers; this points out another difficulty of making global estimates of inputs from all

sources, as the data sets available for or calculated

for each input source may not be directly comparable unless they are based on the same raw data for

the same period of time.

Figure 15.

Estimated Annual Oil Spills From Tankers 1968-1999

– Amounts spilled with >50,000 Tonne-Tanker Spills

Identified (Based on Environmental Research

Consulting Database)

Figure 16.

Estimated Annual Oil Spills From Tankers 1968-1999

– Amounts Spilled and Number of Spills (Based on

Environmental Research Consulting Database)

Figure 17.

Oil Movement By Tankers Worldwide (Millions of Tonnes)

(Brtish Petroleum Data)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 31

Table 22. Inter-area oil movements 1997 (million tonnes)

Inter-Area Oil Movements 1997 (Million Tonnes)

From To

South & Other Rest UnUSA Canada Mexico Central Western Central Africa Australasia China Japan Asia of identi- TOTAL

America Europe Europe Pacific World fied

USA - 7.7 10.7 9.2 9.9 - 0.5 0.8 1.1 2.0 4.1 0.9 - 46.9

Canada 72.7 - - - 0.8 - 0.1 - - - - - - 73.6

Mexico 68.0 1.7 - 5.9 7.9 - 0.8 - - 3.3 - 0.3 - 87.9

South &

Central 132.1 6.1 2.2 - 11.6 - 1.3 - 1.1 0.2 3.8 - - 158.4

America

Western

Europe 32.9 19.1 19.1 1.8 - 10.1 7.4 - 1.0 0.1 4.3 3.0 - 80.0

Former

Soviet 0.6 0.2 - 2.2 90.8 31.8 0.5 - 4.0 0.4 4.8 2.3 30.0 167.6

Union

Central

Europe 0.4 - - - 5.0 - - - - - - 1.4 - 6.8

Middle

East 86.9 5.4 5.4 27.8 187.9 19.3 32.0 9.8 16.7 218.1 294.4 1.4 - 900.7

North

Africa 15.6 3.0 3.0 1.5 97.9 4.0 4.3 - - 1.2 4.4 3.2 - 135.2

West

Africa 68.3 1.2 1.2 14.2 40.1 0.1 0.9 - 5.2 1.4 23.0 - - 154.4

East &

Southern - - - - - - - - - - - - - -

Africa

Australasia 2.4 - - - - - - - 0.3 3.1 7.9 - 2.0 15.7

China 2.2 - - 0.2 - - - 0.2 - 11.5 10.8 0.1 - 25.0

Japan 0.1 - - - - - - - 2.5 - 3.2 0.2 - 6.0

Other

Asia 5.1 - - - 1.6 - - 13.8 25.3 42.2 5.0 0.2 - 93.2

Pacific

Unidentified 2.3 1.8 - - 12.1 - 0.8 2.0 2.1 - 6.4 - - 27.5

TOTAL 489.6 46.2 14.3 62.8 465.6 65.3 48.6 26.6 59.3 283.5 372.1 13.0 32.0 1,978.9

Data from British Petroleum

Figure 18. Major oil trade movements 1997
32 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Table 23. Average annual percentage of oil spilled,

per oil tonnage transported, by tankers

Year Percentage

1974-1977 0.029%

1978-1987 0.022%

1988-1997 0.012%

Source: Etkin 1999c

139 Trends of the amount of oil transported

by tankers that is spilled, expressed as average

annual percentages of the amounts transported

(using BP data, Fig. 18 and Table 22), are shown in

Table 23. Data on petroleum transport were not

available for 1968-1973. The general trend is that

the estimated mean annual percentage of spilled oil

in transit decreased during 1974-1997. During 1974-

1977, the estimated mean annual percentage of oil

transported by tankers that is spilled was 0.029%.

In 1978-1987, the estimated mean annual percentage was 0.022%. From 1988-1997, the percentage

dropped again to 0.012%. Estimates of the percentages of oil spilled will vary based on the source of

the data on amounts of oil transported per year,

being lower if the amounts of oil transported are

taken to be higher. 

140 The reduction in oil spillage from

tankers, despite increases in production and transport during the last ten years, makes the overall

reduction in accidental spillage from tankers more

remarkable. Despite greater opportunities to spill

more oil, i.e. more oil transport is occurring, fewer

spills have occurred and less oil has been released in

accidental spills into the marine environment. This is

due to the efforts of governments, IGOs, and industry. Nonetheless, some of the recent tanker spills

e.g. Erika 1999, Prestige 2002, have involved large

volumes, have caused considerable coastal damage,

and invoked high cleanup costs. Individual spill

events cause many effects and cost a lot for clean up

and compensation.

3.3.4 Regional analysis of accidental spillage data

from all sources 

141 In a study by Etkin (1999e), using the

methodology described in Section 2.3.5, the numbers and amounts of accidental oil spills over 0.17

tonnes were estimated for each region (Figure 6).

The data were revised using information from the

ERC database. The updated numbers and amounts

per region are shown in Figures 19-36. In viewing

these figures, it is essential that the scales of the Y

axis, representing spill number and spill amounts, be

noted carefully when making comparisons between

regions; the scales vary considerably among the 18

regions. 

142 In summary, there is quite different spill

activity in different parts of the world. Some regions

have higher numbers of spills due to their location in

the vicinity of high vessel traffic areas e.g. NW

Atlantic, or due to being areas of high commerce,

tanker traffic, and exploratory and production activities, such as Region 4 (Gulf of Mexico/Caribbean

Sea), Region 7 (the North Sea), and Region 9 (the

Mediterranean). Most spills, particularly from vessels, still occur in port areas or in vessel traffic lanes.

Facility spills and spills from nearshore or shoreline

pipelines also tend to occur in port areas where they

are usually located. Spillage statistics in any one

year can be greatly skewed by the occurrence of one

or more very large incidents. In general, over the last

ten-year period evaluated (1988-97), the occurrence

of accidental spills of all sizes has declined in most

regions compared to the previous two 10-year periods (exceptions being the Black Sea, portions of

Africa, the Persian Gulf and Australia).

143 The history of spills in the 18 global

regions is described below and shown in Figures 20

– 37, on which the notable regional spills are noted.

The regions are:

Region 1 Northeast Pacific Ocean: Figure 19

Region 2 Southeast Pacific Ocean: Figure 20

Region 3 North Atlantic Ocean: Figure 21

Region 4 Gulf of Mexico/Caribbean Sea: Figure 22

Region 5 Southwest Atlantic Ocean: Figure 23

Region 6 Northeast Atlantic Ocean: Figure 24

Region 7 North Sea: Figure 25

Region 8 Baltic Sea: Figure 26

Region 9 Mediterranean Sea: Figure 27

Region 10 Black Sea: Figure 28

Region 11 West/Central African Atlantic: Figure 29

Region 12 Southern Africa: Figure 30

Region 13 Eastern African Indian Ocean: Figure 31

Region 14 Red Sea/Gulf of Aden: Figure 32

Region 15 Gulf Area: Figure 33

Region 16 Arabian Sea/Indian Ocean: Figure 34

Region 17 East Asian/Southeast Asian Seas:

Figure 35

Region 18 Australian/New Zealand Pacific: Figure 36

144 As with the analyses done on accidental

spillages on an international basis, both from specific point sources and from all point source types

added together, spillage in any one year can be

greatly skewed by the occurrence of one or more

very large incidents. The approximate locations of

spills of at least 5,000 tonnes in the last decade

(1988-1997) are shown on the map in Figure 37. The

notable spills in each region are briefly described. 

145 In addition, the estimation technique

results in “zero” values for spill numbers for years in

which there were no reported spills, although it is

likely that there were small spills in those years. In

addition, there are apparent sudden “spikes” in

spillage for years in which a few larger spills were

reported. This is a weakness of this estimation technique. An example of this phenomenon is shown in

Figure 28. The numbers represented in these figures

should only be viewed with regard to general trends

in these regions, due to incomplete data records and

spill reporting.

146 Region 1 (Northeast Pacific Ocean),

while showing an increase in spill number during the
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 33

last period (1988-1997), has had an overall decline in

spillage amounts, as a large amount of accidental

spillage occurred during 1977 (Figure 19). The

exceptionally large 1977 spillage was due to the

106,071-tonne spill from the tanker Hawaiian Patriot

in the Pacific Ocean 590 km off Hawaii.

147 Region 2 (Southeast Pacific Ocean) has

shown little change in the estimated number of spills

during the last period compared to previous years

(Figure 20). However, a considerably smaller amount

was spilled in the last period, after several years of

relatively high accidental spillage during 1973-1980.

The higher spillage can, in large part, be attributed to

the Napier tanker spill of 38,571 tonnes off Chile in

1973, the 35,100-tonne spill from the tanker St. Peter

off Colombia in 1976, and the tanker Caribbean Sea

spill of 32,143 tonnes off El Salvador in 1977.

148 Despite its very high commerce and

tanker traffic, Region 3 (North Atlantic Ocean, i.e.

north-west and north central Atlantic) has shown a

slight reduction in the estimated number of spills in

the last period (Figure 21) compared to the previous

two periods. Estimated spillage amounts have been

relatively low compared to previous years, with the

exception of 1979 and 1988. In 1979, the Atlantic

Empress spilled 141,000 tonnes 800 km east of

Barbados. The tanker Athenian Venture spill and the

large Odyssey tanker spill, both at sea in the North

Atlantic Ocean, contributed 36,000 tonnes and nearly 147,000 tonnes, respectively, in 1988. This region

has also experienced two other spills of at least 5,000

tonnes in the last decade - a vessel spill of 5,000

tonnes in Sandy Hook Channel, New York, USA, in

1988, and the Berge Broker spill of 13,600 tonnes, off

Nova Scotia, Canada, in 1990. The North West

Atlantic’s Grand Banks and Scotian Shelf also experience chronic oiling from ship’s illegal discharges of

waste oils, in unknown quantities but with significant

impacts on pelagic seabirds of hemispheric importance and nearby shorelines (Lock and Deneault

2000; Wells 2001; Wiese et al. 2001; Wiese 2002).

149 The high commerce areas, tanker traffic,

and exploratory and production activities of Region 4

(Gulf of Mexico/Caribbean Sea) continue to experience a high number of spills (Figure 22) each year.

There are an estimated 250 spills each year, although

the numbers have decreased slightly in the last period (1988-1997). Over 50,000 tonnes of spillage

occurred only in 1996. However, the estimated

annual spillage amount in the Gulf of Mexico and

Caribbean Sea still continues to be of concern.

Region 4 is notable for the Ixtoc I exploratory well

blowout in 1979; this spill still holds the record as

being the largest spill from a single point source in

the records since 1959. In addition, during 1979, the

tankers Aegean Captain and Atlantic Empress collided 32 km northeast of Trinidad and Tobago. In this

collision, the Aegean Captain spilled 14,660 tonnes

of oil, while the Atlantic Empress spilled 145,252

tonnes, and an additional 141,102 tonnes while

being towed from the collision site two weeks later;

this incident is also described for Region 3. During

1988-1997, this region experienced three large spills:

17,000 tonnes from the Mega Borg tanker explosion

off Texas, USA, in 1990; a spill of 5,500 tonnes from

pipelines that burst during flooding in the San

Jacinto River estuary in Houston, Texas, USA; and a

spill of nearly 36,000 tonnes from a tanker which

exploded while unloading at a utility plant in

Veracruz, Mexico, in 1996.

Figure 19.

Estimated Oil Spillage in Region 1 (Northeast Pacific

Ocean) (Based on Etkin 1999g; IOSD Oil Spill Data)

Figure 20.

Estimated Oil Spillage in Region 2 (Southeast Pacific

Ocean) (Based on Etkin 1999g; IOSD Spill Data)

Figure 21.

Estimated Oil Spillage in Region 3 (North Atlantic

Ocean) (Based on Etkin 1999g; IOSD Spill Data)
34 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Figure 22.

Estimated Oil Spillage in Region 4 (Gulf of Mexico/

Caribbean Sea) (Based on Etkin 1999g; IOSD Spill

Data)

150 Region 5 (Southwest Atlantic Ocean) has

shown a slight reduction in the estimated annual

number of spills, with between 60 to 155 spills

reported each year (Figure 23). Years 1974 and 1982

showed unusually high spillage numbers. At the

same time, the spills have contributed less than

1,000 tonnes per year. The area had a large spill

from the tanker Metula, which spilled over 47,000

tonnes in the Strait of Magellan, Chile, during 1974;

this spill has been intensively studied (NRC 1985).

This area had one spill of 5,000 tonnes from the

tanker Oshima Spirit, which grounded in the Strait of

Magellan near Punta Arenas, Chile, in 1988. The

year 1997 has two incidences, with the tanker Nissos

Amorgos spill of nearly 3,600 tonnes in Lake

Maracaibo, Venezuela, and the San Jorge spill of

nearly 4,500 tonnes of crude oil in the outer Rio de la

Plata, Uruguay. 

151 There has also been a slight reduction in

the estimated annual number of spills reported in

Region 6 (Northeast Atlantic Ocean) (Figure 24). The

estimated annual amount of oil spilled has increased,

however, since the relatively calm period of the previous decade (1978-87). There were also several

years of high spillage in the 1970s, the most notable

spills being the tanker Urquiola spill of 95,700 tonnes

at La Coruma’s port, Spain, in 1976 and the tanker

Amoco Cadiz spill of 1978 with 233, 565 tonnes off

Portsall on the Brittany coast of France. The northeastern Atlantic region experienced six very large

tanker spills in the 1988-1997 period. These include:

the tanker Marao spill of 5,000 tonnes in Portugal in

1989; the tanker Khark 5 spill of 70,000 tonnes off

the coasts of Morocco and Spain in 1989; the tanker

Aegean Sea spill of 74,000 tonnes in the La

Coruma’s port of Spain, in 1992; the tanker Braer

spill of 83,000-85,000 tonnes in Scotland, United

Kingdom, in 1993; the tanker Sea Empress spill of

72,000 tonnes in the Milford Haven estuary, United

Kingdom, in 1996; and the tanker Bona Fulmar spill

of 6,800 tonnes in the Dover Strait in 1997. Most

recently, the region experienced the Erika spill of

heavy fuel oil off France (1999) and the sinking of the

tanker Prestige, carrying heavy fuel oil, in deep

waters off northwest Spain in November 2002. 

152 The North Sea (Region 7), with its high

tanker traffic and exploration and production activities, continues to experience on average an estimated 100 spills per year in the last period (1988-1997)

(Figure 25). The estimated average annual amount

spilled has decreased from previous decades,

although in 1997 there were over 370 spills and

10,000 tonnes in spillage. The year 1971 stands out

for this region with the very large spillage of 107,100

tonnes in the tanker Texaco Denmark incident off

Belgium. The North Sea region had one spill of at

least 5,000 tonnes in 1993, when the tanker British

Trent spilled 5,100 tonnes off Ostende, Belgium.

This region is, of course, best known for the landmark spill, of the Torrey Canyon on the Cornwall

coast in 1967, which drew so much scientific, public

and political attention to the problem of coastal oil

pollution. Concerns about impacts on seabirds continue, and one study based on beached bird surveys

indicates a decline in chronic oiling in the North Sea

(Camphuysen 1998).

Figure 23.

Estimated Oil Spillage in Region 5 (Southwest

Atlantic Ocean) (Based on Etkin 1999g; IOSD Spill

Data)

Figure 24.

Estimated Oil Spillage in Region 6 (Northeast

Atlantic Ocean) (Based on Etkin 1999g; IOSD Spill

Data)

Figure 25.

Estimated Oil Spillage in Region 7 (North Sea)

(Based on Etkin 1999g; IOSD Spill Data)

153 The Baltic Sea area (Region 8) had

slightly more spills in the last decade (Figure 26).

These spills tend to be small with the total amount of

estimated spillage generally being less than 1,500

tonnes per year. This area experienced no highspillage years in the last period (1988-1997), but did
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 35

have four such years in 1970, 1979, 1981, and 1983.

In 1979, the tanker Antonio Gramsci spilled 4,942

tonnes of oil off Ventspils, Latvia. In 1981, the tanker

Globe Assimi spilled 14,740 tonnes of oil near

Klaipeda, Lithuania. The tanker Bellona spilled

24,684 tonnes of oil in the Kattegat, near Gothenburg

port, Sweden, in 1983. Some of the Baltic spills

have been extensively studied (e.g. NRC 1985).

154 The Mediterranean Sea (Region 9) continues to experience 200 or more of spills annually

(Figure 27), reflecting its high commercial activity. In

fact, the estimated spill number has risen in the last

period compared to the previous ten-year period.

The period 1975 - 1980 was a time of high estimated

spill amounts, attributed to several high-volume vessel spills. In 1976, the tanker Al Dammam spilled

15,714 tonnes of oil in Agioi Theodori, Greece. In

1979, there were two major spills in the

Mediterranean - the tanker Messiniaki Frontis spill of

16,602 tonnes off Crete, Greece, and the cargo carrier Vera Berlingieri spill of 5,940 tonnes off

Fiumicino, Italy. In 1980, the tanker Irenes Serenade

spilled 124,500 tonnes of oil into Navarino Bay, off

Pylos port, Greece. During the last decade, the

Mediterranean Sea experienced two spills over 5,000

tonnes - the Sea Spirit tanker spill of 9,900 tonnes off

Spain in 1990, and the Haven spill of 144,000 tonnes

in Genoa, Italy, in 1991. Oil pollution control has figured prominently in the work of the United Nations

Mediterranean Seas Programme and Action Plan,

with a Regional Oil Combating Center in Malta

(Skjaerseth 2002).

155 The Black Sea (Region 10) has had an

apparent increase in spills in both estimated number

and amount (Figure 28). This may in part be due to

increased reporting from this area since accurate

information was largely unavailable before the 1980s.

There may even have been considerable underreporting during the 1990s. Much of the increase in

spillage can also be attributed to increased shipping,

particularly through the Bosporus Strait, the

entrance into the Black Sea and the site of numerous

collisions and spills. In the last period (1988-1997),

spill number has ranged from an estimated 30 spills

to 95 spills per year, with the largest amount recorded in 1990 when a total of nearly 2,500 tonnes spilled

in 62 separate incidents. Prior to this, the Bosporus

Strait was the site of two very large spills — the 1977

spill of 20,857 tonnes from the tanker USSR 1, and

the 1979 spill of 98,255 tonnes from the tanker

Independentza.

Figure 26.

Estimated Oil Spillage in Region 8 (Baltic Sea)

(Based on Etkin 1999g; IOSD Spill Data)

Figure 27.

Estimated Oil Spillage in Region 9 (Mediterranean

Sea) (Based on Etkin 1999g; IOSD Spill Data)

Figure 28.

Estimated Oil Spillage in Region 10 (Black Sea)

(Based on Etkin 1999g; IOSD Spill Data)

156 Region 11 (West/Central African

Atlantic), the Atlantic Ocean off the west and central

portions of the African continent, has been vulnerable to spills from passing tankers as well as from

spills associated with its own oil production and

transport activities. Nevertheless, this region has

shown a decrease in overall spills in terms of both

estimated number of spills and estimated amount

spilled over the last decade (Figure 29). The year

1991 was a notable exception when the tanker ABT

Summer spilled 51,000 tonnes off Angola. The years

1974, 1979, and 1980 also showed relatively large

amounts of spillage for this region. In 1974, the

tanker Theodoros V spilled 20,857 tonnes 740 km off

Senegal, and the tanker Eleftheria spilled 10,473

tonnes off Sierra Leone. In 1979, the tanker Ioannis

Angelicoussis spilled 31,430 tonnes of oil into the

Cabinda terminal port, in Malongo, Angola. The year

1980 was a particularly bad year with three large

tanker spills — the Salem spilled 16,714 tonnes off

Senegal, the Maria Alejandra spilled 4,187 tonnes of

oil 160 km off Mauritania, and the Mycene spilled

4,187 tonnes off Sierra Leone. In addition, the

Funiwa 5 development well off Forcados, Nigeria,

spilled 28,571 tonnes in a blowout during 1980.

Figure 29.

Estimated Oil Spillage in Region 11 (West/Central

African Atlantic) (Based on Etkin 1999g; IOSD Spill Data).
36 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

157 The southern Atlantic region and Indian

Ocean near the Cape of Good Hope off southern

Africa (Region 12) has shown a slight increase in

estimated accidental oil spill numbers (Figure 30) in

the last ten years. However, the estimated total

amounts spilled each year have consistently been

below 20,000 tonnes. In 1983 this region experienced the largest recorded tanker spill of all time -

the Castillo de Bellver spill of 267,000 tonnes off

Table Bay, South Africa. During the last period

(1988-97), there was one spill over 5,000 tonnes in

this region — the tanker Pacificos spill of 11,000

tonnes in 1989 off South Africa.

158 Region 13, the Indian Ocean off eastern

Africa, is at high risk for spillages due to heavy

tanker traffic passing from the Middle East towards

the Atlantic. This region has shown an increase in

the numbers of spills (Figure 31) with respect to a relative lull in the 1980s, which followed a period of

more spills in the mid- to late-1970s. Between 1988

and 1997, estimated spill amounts were quite low,

with the exception of 1992, when a total of almost

65,000 tonnes spilled in 62 incidents, including the

Katina P. spill of 51,000 tonnes, off South Africa in

the Indian Ocean.

159 The Red Sea and Gulf of Aden areas

(Region 14) are at risk due to high tanker and other

shipping activity through the Suez Canal. This region

has shown a slight decrease in both spill numbers

(Figure 32) and spill amounts in the last period (1988-

1997) compared to previous ones. Since 1988, two

years, namely 1989 and 1990, showed disproportionately high spillage amounts due mainly to two

very large tanker spills.

160 Region 15, the Persian/Arabian Gulf

area, is a notably busy area for tanker transport, oil

terminals, and oil production. Estimated spill numbers have decreased in the last decade compared to

the previous decade (Figure 33), in large part

because the years 1986 and 1987 had so many

tanker incidents related to war action in the 1980-88

Iran-Iraq War. That period (1978-1987) had experienced large amounts of oil spilled in conjunction with

that war and the 1983 Nowruz well blowout that

spilled over 400,000 tonnes into Gulf waters.

Estimated spill amounts have decreased in the last

period (1988-1997) with the notable exception of the

massive spillage that occurred in 1991 during the

Gulf War; an estimated 10,530,768 tonnes of oil from

several terminals, tankers, and other sources reportedly combined to become one massive slick in the

northern Gulf. In addition to the Gulf War spillage,

the only other incident over 5,000 tonnes in the last

decade was the 16,000-tonne spill from the tanker

Seki, which grounded off Fujairah, United Arab

Emirates in 1994.

161 The Arabian Sea and Indian Ocean off

India and surrounding nations (Region 16) experienced a relatively low number of spills in the last 10-

year period (Figure 34), virtually unchanged from the

previous period. The estimated annual spillage

amount decreased slightly in the last period with the

notable exception of two very large incidents off

Bombay, India, in 1989 and 1993. In 1989, the

Puppy P. tanker incident resulted in the spillage of

5,500 tonnes, and an offshore pipeline spilled nearly

6,500 tonnes of oil in 1993.

Figure 30.

Estimated Oil Spillage in Region 12 (Southern

Affrica) (Based on Etkin 1999g; IOSD Spill Data)

Figure 31.

Estimated Oil Spillage in Region 13 (Eastern African

Indian Ocean) (Based on Etkin 1999g; IOSD Spill

Data)

Figure 32.

Estimated Oil Spillage in Region 14 (Red Sea/Gulf

of Aden) (Based on Etkin 1999g; IOSD Spill Data)

Figure 33.

Estimated Oil Spillage in Region 15 (Gulf Area)

(Based on Etkin 1999g; IOSD Spill Data)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 37

Figure 34.

Estimated Oil Spillage in Region 16 (Arabian Sea/

Indian Ocean) (Based on Etkin 1999g; IOSD Spill

Data)

162 In the last period (1988-1997) in Region

17 (East Asian/Southeast Asian Seas), an area of

high commerce, the estimated annual spill number

increased. However, it is not as high as it had been

in the period 1974-1980 (Figure 35). Spill amounts

were also slightly higher during this period, although

again not as high as it had been in the period 1974-

1980. This region experienced nine tanker spills of

at least 5,000 tonnes between 1988 and 1997.

These were: the Century Dawn spill of 10,700 tonnes

in Singapore in 1988; the Vishru spill of 5,280 tonnes

in the Philippines in 1989; the Nagasaki Spirit spill of

13,000 tonnes in the Malacca Strait, Malaysia, in

1992; the Maersk Navigator spill of nearly 25,000

tonnes in the Malacca Strait, Malaysia, in 1993; the

Frontier Express spill of 7,800 tonnes in the Yellow

Sea off South Korea in 1993; the Thanassis A. spill of

37,000 tonnes in the South China Sea off Hong Kong

in 1994; the Nakhodka spill of 6,200 tonnes in Japan

in 1997; the DaQing 243 spill of 17,000 tonnes in the

estuary of the Yanghtze River, China, in 1997; and

the Evoikos spill of 28,600 tonnes in the Singapore

Strait in 1997. 

163 Region 18, the seas around Australia and

New Zealand, had a steady number of spills (Figure

36) over the last two decades, averaging 50 spills per

year. Estimated spill amount has been less than in

other regions with amounts of no more than 1,000

tonnes annually. There were notable exceptions in

1975, which saw the tanker Princess Anne Marie spill

of 14,800 tonnes 700 km off Western Australia, and

1991, which saw the tanker Kirki spill of 17,700

tonnes off Cervantes, Western Australia, which

remains the largest spill in Australia’s history. 

164 Globally, spills occur randomly, with

respect to location, time, volume/amount and type of

oil spilled (Figure 37). However, about half the

regions (3, 4, 6, 7, 8, 9, 10, 12, 13, 15 and 17) are

more oiled recently than others, from ships and other

sea-based activities, and hence at greater risk. Not

surprisingly, these regions have high shipping and oil

production/refining activity.

3.3.5 Sunken vessels

165 Both merchant vessel casualties and

military vessel casualties are in this category of ships

sunken on purpose. Calculating the losses of oils

with accuracy, taking into account all types of oils,

including cargo, for such casualties is virtually

impossible given the variability in ship types, cargoes and absence of records. For example, it is

impossible to know for most casualties exactly how

much oil in each category was onboard the vessels

e.g. how much fuel oil remained, how much waste

machinery oil had been generated. Oil lost with

casualties reported since 1968, particularly for larger

vessels (tankers), will largely be captured in the estimates given in Section 3.3.1 (accidental spillage

from all sources data). For vessels lost before this

date, or for smaller vessels, no reliable estimates can

be derived. Shipping casualty statistics, therefore,

provide only an indication of the potential scale of

the problem. This is, however, far from a trivial issue

from an ecological point of view. Many of the vessels which have floundered and sunk, particularly in

coastal waters, may break up over time, and may

generate mystery spills and pelagic and littoral tar, all

of which pose a risk to marine organisms and public

amenities along the coasts. This is a particularly

acute problem at present (circa 2003) for many

islands in the western Pacific, a long-term consequence of World War II. Continuing work on this

important but poorly documented input source is

discussed later in the report.

Figure 35.

Estimated Oil Spillage in Region 17 (East Asian/

Southeast Asian Seas) (Based on Etkin 1999g; IOSD

Spill Data)

Figure 36.

Estimated Oil Spillage in Region 18 (Australian/New

Zealand Pacific) (Based on Etkin 1999g; IOSD Spill

Data)

3.3.5.1 Merchant vessel casualties

166 In 1997, the number of merchant vessels

in the world fleet was 85,494 (~85,500), with an

aggregate gross tonnage of 522.2 million tons. This

figure considers only vessels above 100 gross tons.

(Lloyds Register, 1998a). This compares to figures in
38 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

the year 1939 of 29,763 vessels with an aggregate

gross tonnage of around 68.5 million tons. Between

1939 and 1997, a total of 21,486 vessels were

recorded as total losses (actual and constructive)

comprising a gross tonnage of 76 million tons

(Lloyds Register, 1991; 1992; 1993; 1994; 1995;

1996; 1997; 1998b). This figure includes merchant

vessels lost as a result of acts of war. This amounted to 5,915 vessels of gross tonnage 25,537,630

tons between 1939 and 1946, approximately a third

of the total. It is not clear whether these figures

include data for the Japanese merchant fleet that

declined from 6.1 million gross tons in 1941 to 1.8

million tons in 1945 (Elting 2000). Casualties occurring in recent years, since 1968 in the context of this

report, which have resulted in the release of oil to the

environment are recorded under Section 3.3.1. 

167 Many vessels were lost with their

remaining bunker, lubricating and hydraulic oils and

with oil (fuel and crude) carried as cargo. Such oils

have the potential to continuously or intermittently

enter the marine environment as a result of deterioration or disturbance of the wreck. This is illustrated

by documented problems with sunken military vessels in Norwegian and United Kingdom waters

(Section 3.3.5.2), and with specific vessels, such as

the Luchenbach off the coast of California, with

chronic leaks and dead oiled seabirds on beaches

(Wiese, pers. comm.), and the barge Irving Whale in

the southern Gulf of St. Lawrence, also with chronic

leaking of oil and persistent slicks killing seabirds.

The Irving Whale sank in 1970 in 67 m of water

(Environment Canada 1996a) and slowly leaked

some 1100 metric tonnes of heavy marine fuel

(Bunker C) oil in the period to 1990 (Environment

Canada 1996b). This comprised some 27% of the

original cargo. The barge lost oil up to the time of

salvage by the government, in summer of 1996.

168 The considerable technical challenges

and costs involved in removing oil cargoes, even

from vessels sunk in accessible waters, are exemplified by the raising of the Irving Whale. The story of

this vessel covered a period of 26 years, involved

a comprehensive operational assessment

(Environment Canada 1996a), and ended with the

wreck being lifted off the bottom in a salvage operation in 1996 at the cost of $CAD 38 million. The

wreck was moved by barge to Halifax, Nova Scotia

where the residual hydrocarbon cargo was recovered

together with some of the PCBs present in the

cargo heating system. The remaining PCBs, now in

the Gulf of St. Lawrence sediments and biota, may

pose a greater risk to marine life than the barge’s oil

cargo (Environment Canada 1996 b).

169 There are a number of difficulties in estimating actual and potential future inputs of oil to

marine waters from lost ships. These include:

.1 Bunker oils and crude oil cargoes are often

recovered from casualties. For example, the

International Salvage Union reported that in

1994, marine salvage companies responded

to over 120 shipping casualties. 1.25 million

tonnes of oil cargoes were salvaged from 14

vessels. A total of 53,000 tonnes of bunker

oils was recovered from an unspecified number of vessels (Lacey, 1995).

Figure 37. Regional Oil Spill Analysis (Oil Spills Over 5,000 tonnes 1988-1997) (Etkin 1999g; IOSD Spill Data)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 39

.2 Over the period 1939-1997, there have been

changes in the fuels used by ships. The initial phase of this period saw the progressive

transition from coal to oil. Subsequently,

there have been qualitative changes in the

grades of fuel oils used by ships. Modern

marine fuel oils are kept liquid by heating the

settling and service tank(s) to approx. 60

degrees C and such oils form sticky masses

when discharged to the sea. Earlier bunker

oils produce thick slicks on seawater with a

low evaporation rate (see Corbett &

Fischbeck, 1997; Hofer, 1999). Accordingly,

there is likely to be variation in the potential

of fuel oils in wrecks to escape to the environment depending upon the characteristics

of the fuel. But as shown by the Arrow

(1970) and Irving Whale (1970) spills in

Canada and the 2002 Prestige fuel oil spill

off Spain (an accident, not a casualty), heavy

oil at great depth still flows and can escape

into the water column and to the sea surface.

.3 Under-reporting of casualties is acknowledged. In particular, casualty returns do not

include ships of less than 100 gross tons,

pleasure craft, naval auxiliaries or ships

restricted to service in harbours or on rivers

and canals (Lloyds Register, 1998a). In addition, casualty returns until 1994 (Lloyds

Register 1994) explicitly state that losses in

the smaller gross tonnage ranges (100-499

and 500-999 gross tons) are probably understated. The smaller vessels, nonetheless,

may contain significant quantities of oil. Two

fishing vessels of 87 and 76 gross tons, each

reported as casualties in 1997 in Scottish

waters, resulted in the loss of 10 tonnes of

marine fuel oils contained in their fuel tanks.

In other incidents in Scottish waters in 1997,

small fishing vessel casualties lost at least

19.5 tonnes of fuel oils to sea (ACOPS 1998)

after the vessels floundered. It was not possible in this study to calculate the total oil

inputs from such casualties worldwide.

.4 Casualty returns include both constructive

and actual total losses. Constructive losses

may subsequently be broken up or repaired

and returned to service. In these cases,

hydrocarbon contents are not necessarily

lost to sea. 

.5 Casualty returns include details of the ship

type (e.g. oil tanker, bulk carrier) but not of

the cargoes and bunkers carried at the time

of the loss.

3.3.5.2 Military vessel casualties

170 Military vessels (i.e. naval ships) lost at

sea, including those lost in combat, are excluded

from the annual reporting through Lloyds Register of

Shipping. Nonetheless, some collated records exist

for some military craft for WWII (1939-1945) and subsequent years. These show that between 1939 and

1945, some 104 French military vessels were lost at

sea (164,369 tons) and a further 99 scuttled (196,251

tons) (Couhat 1971). Equivalent figures for German

vessels between 1939 and 1947 are 841 (1,040,000

tons) lost and 365 (426,000 tons) scuttled (Taylor

1966). Between 1939 and 1959, 1,577 United

Kingdom fighting ships were lost at sea (1,746,000

tons) and 21 were expended as targets or scuttled

between 1940 and 1961 (41,290 tons) (Lenton &

Colledge 1964). The bulk of fighting vessel losses

occurred as a result of conflict. Although these data

are incomplete with respect to information for inter

alia the Imperial Japanese Navy (estimated losses of

302 vessels), the US Navy (estimated losses of 146

vessels) (Elting 2000), and British Commonwealth

Navies operating as part of the United Kingdom

Royal Navy, they illustrate that the aggregate tonnages are a relatively small proportion of merchant

shipping tonnages lost over the same period.

Evaluation is also made difficult by the fact that numbers and tonnages are approximate only. Smaller

vessels and landing craft may not be included other

than in the figures for the United Kingdom Royal

Navy. An unrecorded number of ships were transferred between national navies (e.g. USA to Canada)

or raised after scuttling (and sometimes re-sunk

thereafter). Tonnages, moreover, may be given as

registered or displacement, with warships given as

standard rather than displacement tonnages according to class and submarines as surfaced rather than

submerged displacement.

171 Nonetheless, military casualties are documented for causing significant releases of oil into

marine ecosystems. For example, the German naval

vessel Blucher was sunk in the Oslofjord, Norway, in

1940. Following chronic leakage of bunker fuel over

a number of years, an operation was carried out to

tap and drain the tanks. Recovery of this oil was

completed in 1995. Details of the operation were

summarized by the Norwegian State Pollution

Control Authority (SFT 1995). More recently, the oil

cargo on a naval oil tanker USS Mississinewa, sunk

in 1944 within Ulithi Lagoon in the NW Pacific and

leaking after a cyclone, was recovered (ASA 2003).

ASA (2003) also reports the presence of another

1800 known WWII wrecks in the South Pacific alone,

loaded with oils, chemicals and ordnance. 

172 In United Kingdom waters, the wreck of

HMS Royal Oak, a major second world war casualty

sunk in October 1939, has been identified as a continuing source of beach pollution to Scapa Flow, an

anchorage in the Shetland Islands (ACOPS 1998).

Subsequent anecdotal evidence (Orcadian Daily

News 2000) indicated that some 1000 tonnes of oil

were contained in the wreck and were leaking at a

rate of between 300-500 litres per day. Efforts to tap

into the hull and remove the oil are planned following

the failure of hull patches and collection devices to

contain the oil. However, the planned operations are

complicated by the fact that the wreck is a designated war grave for the 833 men killed when the vessel

was torpedoed and sunk. 
40 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

173 In general, reliable estimates of actual

and potential oil losses to the marine environment

from military vessel casualties are rendered impossible by the same factors that apply to merchant vessels. Records are unlikely to exist of smaller casualties such as landing craft and barges and while WWI

& II Allied losses are likely to be well documented,

the same is not true of vessels lost by the other combatants e.g. in the Pacific theatre. In addition and

not surprisingly, no reliable records of bunker contents at the time of the sinking exist. Finally, a large

number of ships were scuttled at the end of both

WWI and WWII as part of disarmament programmes

and also to dispose of surplus munitions and chemical weapons. However, it seems probable that

bunkers were largely emptied prior to scuttling, and

some of the vessels were towed to the sites where

they were scuttled. 

174 As noted above, the occurrence and

location of sunken vessels is also linked to the

occurrence of pelagic and littoral tar (Section 5.8).

The tar may be coming from both historic ship losses (i.e. marine casualties as discussed above) and

the operation of ships today. Distinguishing between

“old” and “new” sources of oil is now possible using

modern, oil chemistry, fingerprinting techniques

(Page et al. 1995, and others). This becomes important if tar amounts and distributions are used to

monitor ship pollution and/or the effectiveness of

MARPOL and other regulatory instruments, i.e.

coastal oiling may reflect old wrecks still containing

oil cargo or bunkered fuel oil, rather than or in addition to existing oiling events.

175 In general, therefore, it is not possible to

derive reliable estimates for oil lost at sea by marine

casualties and the annual inputs coming from these

sources. Some indication of the scale of the problem can be determined by simply assuming that a

fixed amount of oil has been lost with each vessel.

Given the total casualties of approximately 23,000

ships since 1939, and assuming that between 1

tonne and 100 tonnes of oil was lost with each

wreck, results in an aggregate estimate of between

23,000-2.3 million tonnes of total oil lost at sea with

these vessels. The accuracy of these estimates is

impossible to ascertain, but even the upper bound

value is plausible.

176 Given their frequent location near coastlines and the aging condition of the wrecks, further

research should be immediately directed to quantifying the oil input from war-related casualties (sunken

vessels) with greater precision, and the degree to

which this poses a future risk to the marine environment.

3.4 Dry docking of ships

3.4.1 Tankers

177 NRC (1985) and MEPC (1990) determined that some 4,000 tons of oil discharges were

coming from dry-docking. Since the 1990 report, a

number of changes have again occurred which

would affect these estimates, such as the Enhanced

Survey Program (ESP) that sets tighter requirements

for oil tankers and dry bulkers.

178 For the majority of dry-dockings, it will

not be necessary to clean the cargo tanks. Twice

every 5 years, according to current regulations (circa

2003) (T.J. Gunner, pers. comm.), tankers have to

visit a repair yard with dry-docking facilities in order

to re-coat their anti-fouling system. Also, it will not

always be necessary to desludge all tanks at a single

dry-docking.

179 Notwithstanding MARPOL 73/78’s

improvement of enforcement procedures, oil refineries now require tankers to carry out the minimum

COW requirements as provided in MARPOL. The

application of COW removes sludge from a tanker’s

cargo tanks, so that it may be discharged to shore

receiving tanks. The minimum COW requirement is,

on average, 60% of the cargo tank capacity for the

non-SBT tankers and 25% for the SBT and double

hull tankers. The vessel will normally perform tank

cleaning while on a ballast leg of a voyage, or while

en route to the dry dock.

180 Taking into account the above factors, it

is estimated that of the world’s tanker fleet of 321.1

million dwt (circa 2001), 2% of the tankers discharge

sludge/slop amounting to 0.2% of their dead weight

prior to and during their dry-docking. Under MARPOL 73/78 regulations, this waste should be disposed of at shore-based reception facilities. Owing

to the lack of statistics on delivery of slops to these

facilities, 0.2% remains as the worst-case discharge

scenario. This figure was 0.2% in the 1990 report

(MEPC 1990); owing to increased efficiency in COW,

there is no reason to believe that this will have

increased. Dry docking intervals would be twice

every 5 years. Hence, the annual discharge of oil

that is discharged into the sea from dry docking of

tankers becomes:

321.1 million dwt x 0.02 x 0.001 x 12/30 = 2569

tonnes/yr. or ~2600 tonnes/yr.

3.4.2 Other vessels

181 MEPC (1990) does not deal with other

vessels, on the assumption that the quantity of oil

discharged into the sea from such operations would

be negligible. Under the IMO’s Enhanced Survey

Programme (IMO Assembly Resolutions A.744 &

A.746), dry bulker ships (totalling 8680 in number,

Fairplay Database 2000) will be subjected to stricter

maintenance programmes than in earlier years,

hence requiring more hot work, i.e. structural work

with torches, adjacent to fuel oil tanks. These tanks

will thus need cleaning and gas freeing for hot work.

Thus, it is reasonable to expect that 2% of the dry

bulkers will discharge approximately 10 tonnes

sludge and tank washing prior to dry-docking, or

upon entry into the dry-docking yards. Again, this is

the worst-case scenario owing to the requirement
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 41

under MARPOL to unload waste oils at the dry dock

or to a reception facility on shore. The annual discharge due to dry-docking into the sea then

becomes:

8680 ships x 10 tons x 0.02 x 0.2 = 347 tonnes/yr.

or 350 tonnes/yr.

In summary, the total oil discharge during dry docking = 2916 tonnes/yr. or 2900 tonnes/yr.

3.5 Recycling of ships

182 In this study, the term ‘ship recycling’

applies to the breaking up and dismantling of ships

at the end of their useful life. In the majority of

cases, this is carried out on beaches on the Indian

sub-Continent. Furthermore, as issues of concern

under IMO and ILO bodies, the practice of “ship

scrapping” has been referred to as “Recycling”. This

is further validated as it is estimated that 95% of a

vessel will be reused or recycled.

183 The focus on ship demolition is now

placed on beach operations as recycling sites, rather

than on berth operations. Recycling is very labourintensive and there is very little concern for workers’

safety and protection of the environment. Workers

are exposed to many toxic chemicals and fumes,

there are physical hazards, and chemicals enter the

local air and water. Bangladesh, China, India,

Pakistan and Vietnam are the main breaking centres,

using beaches and cheap labour. Health and environmental issues associated with recycling are now

being actively addressed through IMO. 

184 When a single hulled, non-STB tanker

reaches 25 years of age, it will have to be upgraded,

or proceed to demolition. When this category of

tanker reaches 30 years of age, it can no longer

trade, and will go for demolition. Thus, a massive

scrapping or recycling of tankers can be anticipated

in the coming years. INTERTANKO estimates that 25

tankers will be phased out in 2003, 97 in 2004, 142

in 2005, 134 in 2006 and 71 in 2007 (Hydrostatic

Balance Loading Publication, August 1997), a total of

469 tankers over 5 years.

185 Ships going for demolition in India will

need to arrive gas-free (i.e. slop-free) for hot work.

Those proceeding to Pakistan and Bangladesh can

be delivered ‘gas-free for tank entry’; that means the

ships are not cleaned out and thus they will have

sludge and oily residues onboard. This condition

can be obtained by slightly ballasting cargo tanks.

Tankers sold for demolition are mostly cleaned and

made slop free using facilities that are available in

Fujairah (United Arab Emirates) and Singapore. To

become gas-free, large tankers will normally generate between 500 to 1000 tons of slops for delivery to

reception facilities. These slops have a commercial

value.

186 Two categories of oil can be established

to calculate the quantities of oil discharged into the

marine environment during scrapping operations:

.1 fuels, hydraulic oils and lubricating oils (all

ships); and

.2 cargo residues and oil sludge (tankers).

3.5.1 Hydraulic oils, lubricating oils and fuels (all

ships)

187 Hydraulic and lubricating oils have a

considerable second hand value owing to their initial

high cost. They are being recovered from the ships

for resale (DNV 1999). Two types of fuel will remain

on board when a vessel is sent for recycling, fuel oil

for the main engines and marine diesel oils (MDO) for

the generators. The majority of breaking yards specify a common quantity to be available on board the

vessel before it is beached. Common requirements

call for one day’s worth of fuel oil (estimated at 60

tonnes for a diesel engine VLCC) and 8 days worth of

MDO to be on-board when the vessel is to be

beached.

188 Owing to the high value of the fuel oil

(US$180/tonne, based on 2000 figures), fuel oil will

be recovered for re-sale and re-use. The MDO will

be used up on board during the breaking procedure

to run generators for powering tools and lighting.

What remains after breaking will be transferred and

used for smaller generators on shore or will be sold.

189 The engine waste oil (i.e. oil sludge)

remaining on board would be found in the sludge

tank. This would have little or no value and would

need to be disposed of elsewhere. It can be

assumed that the majority of the oil sludge would

end up in the marine environment. In the 1999

DNVPS study, it was estimated that for a 290,000

dwt tanker, some 5m3

(4.5 tonnes) of oil sludge would

remain in the sludge tank. Alternatively, this can be

expressed as 0.00156% of oil sludge per ship and

applied to the year 2000 dead weight numbers, i.e.

21.2 million dwt. Thus, the amount of oil disposed

of, from all ships while being recycled, is:

21.2 million dwt* x 0.0000156 = 330 tonnes/yr.

(*estimated dwt of all ships being recycled per year)

3.5.2 Cargo residues/oil sludge (tankers)

190 Industry sources state that an average

VLCC has some 600 tonnes of oil, mixed with sand

and rust, remaining in its cargo tanks. Based on the

DNVPS figures for a VLCC, this equates to 0.2% oil

cargo remaining on board a tanker before being sent

for recycling. On the basis that:

1. some of this oil has some residual value and

is received by the breaking yard for re-sale

or re-use; and

2. tankers being sent for scrapping in locations

requiring gas-free conditions have to remove

most, if not all, oil residues in the cargo

tanks (in 2000, 38% of tankers went for

scrapping in India where legislation requires

gas freeing), there is approximately 50%
42 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

removal of the waste cargo oil. This would

bring the percentage estimate in line with

MEPC (1990), where 0.1% waste oil from

each tanker cargo was calculated as discharged into the marine environment. The

following estimation, using year 2000 tanker

scrap numbers from Intertanko, i.e. 14.5 million dwt, can be given for cargo oil entering

the marine environment during recycling:

14.5 mill dwt x 0.001 = 14,500 tonnes/yr.

191 The estimate of total oils (of all types),

therefore, entering the marine environment from ship

scrapping and recycling is: 14,830 tonnes/yr. or

14800 tonnes/yr.

3.6 Operational discharges from ships

operating under sovereign immunity

192 Under Article 96 of the United Nations

Convention on the Law of the Sea (UNCLOS, 1982),

ships owned or operated by a State and used only

on governmental non-commercial service “shall, on

the high seas, have complete immunity from the

jurisdiction of any State other than the flag State”.

More obviously, warships on the high seas also have

complete immunity under Article 95 of UNCLOS.

Each State is expected to act in accordance with

treaty provisions for the protection of the marine

environment. For this study, it has been impossible

to find data that relate specifically to this area only,

i.e. oil discharged on the high seas during routine

operations of all types of vessels operating under

sovereign immunity. Moreover, it is assumed that the

discharges of these vessels have already been

included under other inputs in this report, and would

likely be negligible to prevent detection.

3.7 Deliberate discharges of oil to save

life at sea

193 Under the MARPOL 73/78 Convention

(IMO 1997a), steps taken to save life at sea include

the deliberate discharge of oil if required, i.e. oil can

dampen wave activity around a stricken boat or vessel. While this practice is not banned under the convention, there are no reliable records of this type of

incident. It is believed that this type of discharge

occurs very rarely, if it occurs at all, therefore, for this

report the annual input is assumed to be zero. 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 43

4.1 Introduction

194 The development of established hydrocarbon reservoirs and the identification and development of new ones continues to play a major role in

the oil and gas sector. Between 25 and 30% of global production is estimated to come now from offshore reservoirs, with the principal producing areas

being located in the Gulf of Mexico, the North Sea,

Brazil and West Africa. There is also offshore production in Southeast Asia and Australia.

Technological advances in surveying, drilling and

production have allowed a substantial move to deepwater locations; these fields are likely to become

more important in future years.

195Some 6,000 oil and gas installations are

presently operating in the marine environment.

These include fixed steel and concrete structures,

floating steel and concrete structures, and sub-sea

production units. Many of these structures are

manned; however, a significant number are unmanned. The fixed and floating structures range in

size from a few thousand tonnes, to in excess of half

a million tonnes for the large concrete structures,

e.g. Hibernia, and structures placed in sea areas

prone to seasonal ice and icebergs e.g. off

Newfoundland. More recently, with the advent of

deep water technology, there has been a move away

from traditional structures fixed into the sea-bed to

custom built, Floating Production, Storage and

Offloading units (FPSOs) which, though anchored at

a production site, are capable of being moved to different areas more easily than ‘conventional’ structures. The global distribution of platforms in the

marine environment is shown in Figure 38. By far the

greatest number of installations (>4000) is located in

the Gulf of Mexico, with smaller numbers in other

producing areas. Figure 38 does not identify production platforms in Atlantic Canada (ie Scotian

Shelf and Grand Banks, with at least 7 platforms to

date). 

196 Exploration for and exploitation of offshore hydrocarbon reserves have a number of discrete phases. Surveying the underlying geological

structures involves non-invasive acoustic techniques; there are no releases of hydrocarbons during

this phase of the process. Following identification of

potential deposits, exploratory drilling may be initiated to determine whether there are economically

recoverable hydrocarbons in the prospects. During

exploration drilling, cuttings contaminated with oilbased drilling fluids may be discharged to the sea,

although it is frequently in the companies’ economic

interests to maximise the re-use of otherwise expensive drilling fluids. During appraisal drilling and possibly during extended well testing, produced fluids

(Gas and Oil) may need to be flared for safety reasons. Further releases of contaminated cuttings can

be expected during both appraisal drilling and eventually from the development of production well systems. However, the major discharge of hydrocarbons will take place during the production phase.

There are no collated data on hydrocarbon discharges during exploration drilling with which to

develop a global input estimate.

4.2 Operational discharges from

offshore installations

4.2.1 Machinery space discharges

197 Discharges of oily water from machinery

spaces fall under the purview of MARPOL 73/78,

except where stricter national regulations apply.

This imposes a concentration standard and disposal

requirements in relation to rate of release and dilution. Such discharges are thought to be minimal.

4 EXPLORATION AND PRODUCTION IN THE OFFSHORE

Figure 38. Worldwide distribution of offshore oil and gas platforms (circa 2000)
44 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Consequently, there appears to be no requirement to

report monitoring data to regulatory agencies. In

some instances, for operational reasons, drainage

space discharges are blended into produced water

streams and are treated in that process train.

4.2.2 Drilling discharges

198 Drilling fluids play essential roles in providing for the safety and effectiveness of the drilling

process. Drilling fluids are the means for maintaining

pressure on the formations being drilled, removing

cuttings from the borehole, protecting and supporting the borehole wall, protecting permeable zones

from formation damage, and cooling and lubricating

the drill bit and drill string.

199 Three basic types of drilling fluids are

currently in use: water-based fluids, oil-based fluids

and synthetic-based fluids. Oil-based fluids are

used when drilling conditions require more stabilization of the borehole, greater lubricity, and more

resistance to thermal degradation than are provided

by water-based fluids. They are often used where

specific problematic formations may be encountered. Oil-based fluids are frequently used in offshore drilling operations because the well paths are

deviated, rather than vertical, in order to reach distant parts of the reservoir from a fixed drilling location. Deviated wells typically have increased requirements for lubricity and well bore stability compared

to vertical wells.

200 Almost twenty years ago, concern was

expressed that diesel oil-based drilling fluids had

adverse effects on the marine environment. In some

producing areas, these concerns initiated regulatory

action to curtail their discharge16. As a consequence

of these regulatory activities, discharges of cuttings

contaminated with diesel oil-based mud have almost

completely ceased in the areas covered by those

regulations (see Table 24). Moreover, oilbased muds,

introduced as substitutes for diesel-based systems,

have also fallen under regulatory control.

201 The phase out of the discharges of oilcontaminated cuttings in the North Sea is illustrated

in Table 24 (data compiled by OGP 1999) and Figure

39.17

202 Data on use and discharge of cuttings

contaminated by oil-based muds are not available

for other producing areas, beyond Europe, North

America and Australia where both use and discharge

have almost ended.

Figure 39.

Inputs of oil on cuttings into the North Sea

4.2.3 Produced water discharges

203 Water occurs naturally in geological oil

reservoirs and is extracted from formations along

with the hydrocarbons. Produced water and hydrocarbons are separated at the site of production by

physical and chemical techniques. The water phase

may be re-injected into the reservoir to maintain

pressure and thereby to enhance recovery. At some

locations, where the subterranean geology permits,

produced water can be re-injected as a means of

disposal. However, for geological and other reasons,

this is option is not widely available, and treated produced water containing small (103 x ambient)

amounts of dispersed and dissolved oil is most often

discharged at sea (Neff 2002; Lee et al. 2005).

204 In the initial stages of exploiting a hydrocarbon deposit, production water volumes may be

low. As the field matures, however, volumes of production water usually rise and in mature areas, water

amounts of in excess of 90% are not unusual.

205 In many producing areas, local and/or

regional regulatory authorities have imposed a quality standard for oil in produced water. Numerical

standards range from approximately 30 mg oil per

litre of produced water, to approximately 100 mg l-1

.

Table 24. Input of oil into the North Sea of oil-based fluids on drill cuttings, in tonnes

Year 1989 1990 1991 1992 1993 1994 1995 1996 1997

Oil on cuttings

- tonnes 14,248 12,385 10,332 6,089 3,948 3,820 3,180 3,826 ?

16 In the case of drilling discharges, ‘oil’ released refers to oil

used in the drilling fluid and not fluids arising from the formations being drilled.

17 In 2000, the OSPAR Commission covering the Northeast

Atlantic, including the North Sea, adopted a Decision which

prohibits the discharge of cuttings contaminated with OilBased Muds, unless the concentration of fluid on cuttings is

less than 1%.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 45

In others, discharge targets or standards have not

been established. However, it is clearly in the operators’ interests to maximize the separation of oil

(product) from water, if only from an economic perspective. Care must be taken, however, in making

direct comparisons between the numerical standards

defined in different regions. Since oil is a complex

mixture of organic components, analysis of oil in

water is non-specific and results of determinations

will be dependent upon the analytical method used.

Thus, numerical differences in standards do not necessarily reflect different regional views on environmental protection. Consequently, for this and other

reasons, care must be taken comparing and combining input estimates from different producing regions.

206 There are relatively few comprehensive

records of discharges of oil in produced water that

can be incorporated into this study. However, those

that are available (e.g. Neff 2002) cover the principal

offshore production provinces and can indicate the

relative magnitude of oil from offshore E&P activities

in relation to other sources.

207 Data from the United States Minerals

Management Service (USMMS) (Dannenberger, pers.

comm. to J. Campbell) for the Gulf of Mexico show

that, in 1996 and 1997, the input of produced water

into the marine environment was approximately 72

million cubic metres. Less than 5% of produced

water that was generated was re-injected into the

reservoir. The produced water volume equates to an

annual oil input of approximately 2,900 tonnes,

assuming an oil content of 40 mg oil per litre of

water.18 In Australia, average annual releases of oil in

production water have been estimated as 1,450

tonnes (again on the basis of a mean concentration

of 40 mg oil per litre of water).

208 In the North Sea, oil-producing reservoirs are approaching maturity and volumes of produced water are increasing. Very little produced

water is re-injected into formations for disposal purposes. Figure 40 shows the increase in volume of

produced water discharged over the last seven

years. Inputs of oil to the North Sea via produced

water discharges are shown in Table 25 and Figure

41. Predicted increases in the volume of produced

water can be translated into predictions of oil input

to the North Sea of around 12,000 tonnes (by 2002).

Figure 40.

Produced water discharge to the North Sea

Figure 41.

Input of oil from produced water discharges to the

North Sea

209 The input data reported above reflect the

situation in only a portion of the offshore producing

areas – the Gulf of Mexico and the North Sea. Data

are unavailable in published form for other producing

areas, making it difficult or impossible to extrapolate

to global input estimates. Amounts and composition

of production water will vary from reservoir to reservoir, within reservoirs and as the reservoir matures

(Neff 2002). In relation to produced water, for example, it is necessary to understand the profile of water

production in each of the areas for which data have

not been available. Moreover, the data for some

areas where reports are available are largely worst

case estimates, since calculations of load have

assumed discharge at the existing regulatory limit.

Table 25. Oil inputs to the North Sea from discharges of produced water

Year 1989 1990 1991 1992 1993 1994 1995 1996 1997

Oil discharge

- tonnes 4119 5058 5289 5572 5108 5589 6998 7465 8109

18 Data supplied by the United States Environmental Protection

Agency conflict with MMS data. Total volume of produced

water discharged annually is estimated as twice that provided by MMS.
46 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Improving the quality and coverage of the data

requires more thorough involvement of the regional

regulators, industry associations and oil companies.

This presupposes that the appropriate data are

required to be collected, i.e. that there is a regulatory requirement. There are also constraints on extrapolating input information on discharges of drilling fluids associated with cuttings. The most reliable information will be obtained on a field-by-field basis.

210 In 1997, the governments of Netherlands

and Brazil co-hosted a conference of international

experts on the effects of offshore activities on the

environment. The conference was an initiative under

the umbrella of the United Nations Commission on

Sustainable Development. A major outcome of this

conference was the recognition that greater transparency was required of offshore activities. The Oil

and Gas Industry is currently considering the mechanisms by which this transparency might be

achieved, including the development of performance

indicators that are likely to include input statistics.

211 Using the above average figures from

the Gulf of Mexico (2,900 tonnes/yr.), Australia (1,450

tonnes/yr.), and the North Sea (12,000 tonnes/yr.),

the total estimated annual input of oil from offshore

operations into the sea is estimated to be 16,350

tonnes/yr, or ~16,400 tonnes/yr.

4.2.4 Air emissions (Non-methane volatile organic

compounds or VOCs)

212 Since the extraction and processing of

offshore oil deposits is a ‘closed’ system, losses of

volatile components (VOCs) are considered to be

minimal. Sources are the occasional venting and

flaring of gases accumulated during the production

process or during handling of the processed crude

oil. Losses of VOCs during transfer of oil to cargo

tankers are addressed in Section 3.1.6 and 3.1.7. 

4.3 Accidental discharges from

exploration and production activities

213 The estimated annual number of accidental marine spills from exploration and production

activities, including spills from platforms, wells and

rigs, but not including offshore pipelines (included in

Section 4.4.2), and the amounts spilled from these

sources, are shown in Figure 42. The largest known

spillages from exploration and production sources to

date occurred in 1979 and 1983. The 1979 spill was

caused by the Ixtoc I exploratory well blowout; a

total of 476,190 tonnes of oil spilled into the Gulf of

Mexico off Ciudad del Carmen, Mexico, over 295

days. This is the largest spill from a single point

source in recorded history. In 1983, the Nowruz well

blowout in the Nowruz Field of Iran poured a total of

272,100 tonnes of oil into the Persian Gulf over 196

days. These spills were so large that each day of oil

release was an amount equivalent to a significant

ship spill. Each of these two blowouts is treated in

this analysis as one continuous release and hence as

one spill incident. Spillage rates for the Ixtoc I well

blowout were estimated at 4,300 tonnes per day for

the first 10 weeks of the spill. The spillage rate then

slowed to 1,429 tonnes per day for three months

after relief wells were dug. The rate slowed to 285

tonnes per day for the next three months, then to 57

tonnes per day for the last three weeks before the

well was finally capped. Similarly, the Nowruz well

released oil at a rate of 571-1,429 tonnes per day

until it was capped six and one half months later.

Data on such releases are generally self-reported

estimates from industry, and seldom are ranges or

confidence limits provided.

Figure 42.

Estimated Annual Oil Spills From Exploration &

Production Facilities 1968-1999 (Based on

Environmental Research Consulting Database)

214 Catastrophic exploration and production

activity spills, such as the Ixtoc I spill of 1979-1980

that involved the spillage of more than 476,000

tonnes of oil, are even more rare than extremely large

tanker spills. Although it was a rare event (one in 35

years), the Ixtoc I spill was the largest total amount

of oil released from one man-made point source in

recorded history. While the likelihood of another,

extremely large, well blowout is extremely small and

has been vastly reduced by current methodologies

and technology, the possibility still exists and should

be borne in mind. No very large exploration and production spills over 5,000 tonnes occurred in the period 1988-97. 

215 While there have been no marine production and exploration spills over 2,000 tonnes during the past decade (the 1990s), there have been

seven spills over 350 tonnes during this time period,

all but one in the North Sea. In 1988, the Piper Alpha

rig exploded in the North Sea off Aberdeen,

Scotland, United Kingdom, spilling 750 tonnes of oil

directly to the sea. Later that same year, a floating

production platform spilled 1,500 tonnes in Fulmar

oilfield, in the North Sea, off the United Kingdom. In

1990, a well in the Troll offshore oilfield in the North

Sea, off Norway, spilled 361 tonnes during well testing. In 1992, a platform in the North Sea Statfjord oil

field spilled 827 tonnes of oil off Norway due to an

operational error. Also in 1992, the Greenhill

Petroleum production well blowout off Timbalier Bay,

Louisiana, USA, spilled 1,600 tonnes of oil into the

Gulf of Mexico. Another North Sea platform spilled

500 tonnes in 1995 off Germany after structural damage by field operators. In 1997, a floating storage
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 47

platform named the Captain Field spilled 680 tonnes

of oil in the North Sea in the United Kingdom sector

of the North Sea.

216 The analysis resulted in an average input

of 600 tonnes/yr. into the marine environment from

accidental releases from exploration and production

activities during the years 1988-1997. There is no

additional breakdown for larger spills since there

were no spills in this range from exploration and production activities during this time period.

4.4 Pipelines

4.4.1 Operational discharges

217 Pipeline transmission of oil from offshore

production sites to coastal refineries and distribution

installations in some areas represents a major means

of delivery. For example, almost 60% of the oil produced in the North Sea is delivered to land via

pipeline. Operational discharges of oil from pipelines

are small and occur during commissioning, maintenance and decommissioning phases. There are no

published data available for routine, accidental discharges from pipelines. Major releases only occur as

a result of accidents.

4.4.2 Accidental releases from pipelines

218 Figure 43 shows the estimated annual

number of oil spills and amounts of oil spilled into

the marine environment from accidental releases

from offshore or coastal pipelines. The annual estimate of oil input during the period 1988-1997 is

2,800 tonnes. This spillage represents a slight

increase in estimated annual amounts spilled compared to the previous two time periods, in which

1,800 tonnes of oil spilled annually from pipelines in

1968-1977 and 2,100 tonnes spilled annually in

1978-1987. The lower input values from the first

time period are in large part due to incomplete

reporting of pipeline spills. At the same time, estimated numbers of spills have risen sharply from an

average of 47 spills per year in 1968-1977, to 188

spills per year in 1978-1987, to 228 spills per year

during the last decade. This apparent increase in

numbers of pipeline spills needs further examination.

219 During 1988-1997, there were two offshore or coastal pipeline spills that involved more

than 5,000 tonnes. There was a spill of 6,463 tonnes

after an offshore pipeline ruptured in the Arabian Sea

off Bombay, India, in 1993, and a spill of 5,497

tonnes of oil from several pipelines in the San

Jacinto River estuary in Houston, Texas, USA, after

flood damage in 1994. Relative to catastrophic vessel spills, such pipeline spills are rare, comprising

only 4.9% of spills over 5,000 tonnes in the last 10-

year period.

220 Prior to this period (1988-97), three other

very large marine pipeline spills were reported: a spill

of 22,950 tonnes into the Gulf of Mexico, after a

ship’s anchor damaged an offshore pipeline off

Grand Isle, Louisiana, USA, in 1967; a rupture of a

coastal pipeline that spilled 14,290 tonnes of oil into

Tarut Bay, Saudi Arabia, in 1970; and a coastal

pipeline rupture into the Mediterranean Sea at

Bahce, Turkey, in 1982. Large pipeline spills

occurred during 1998 in both Nigeria and Brazil,

accounting for the large peak in that year; these incidents are not included in the overall spill input analysis which was limited to 1988-1997.

221 Taking into account inputs from these

larger incidents, the pipeline input estimates are as

follows:

900 tonnes/yr. in <5,000-tonne spills 

plus an average of 1,900 tonnes/yr. in spills >5,000

tonnes

for an overall average input from pipelines of 2,800

tonnes/yr.

Figure 43.

Estimated Annual Oil Spills from Marine Pipelines

1968-1999 (Based on Environmental research

Consulting)

4.5 Offshore exploration and production

- summary

222 The estimated annual inputs of oil from

offshore exploration and production are 19,750

tonnes/yr. or ~20,000 tonnes/yr. This is certainly

an under estimate of unknown magnitude, due to the

absence of data from many areas of the world where

the offshore industry is operating under less

demanding regulatory regimes than in the North Sea

and the Gulf of Mexico, the areas upon which the

input numbers were estimated.
48 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

5.1 Coastal refineries, oil storage

facilities and marine terminals

5.1.1 Operational oil inputs from coastal refineries

223 Some oil and oil-derived compounds

leave refinery facilities in wastewater effluents. This

is water that is extracted from the crude oil itself or

is used in various processes in the refinery.

Concentrations of oil in the effluents are generally in

the order of several parts per million (ppm, measured

as total oil and grease, or as total petroleum hydrocarbons). Oily effluents can be treated in wastewater

treatment systems and/or by oil/water separators

before the water is introduced into the receiving

estuarine or coastal environment. 

224 Many countries have laws and regulations limiting the amount of oil that can be present in

such effluents. Not all refinery operators abide by

these rules and enforcement of regulations varies by

location. Theoretically, the amount of waste oil that

enters the sea from refinery effluents should be minimal in a fairly modern and well-maintained facility.

In most developed countries, the effluents contain on

average 5 ppm of oil. In developing countries and

countries with refineries that are not well maintained

or are operated under compromised conditions, oil

concentrations in the effluents are often as high as

25 ppm.

225 An estimate of the total amounts of oil

entering the marine environment due to operational

spillage from coastal refineries is shown in Tables 26

and 27 for coastal countries having refineries and for

the 18 regions shown in Figure 6. Estimates are

based on the total crude refining capacities of

coastal or estuarine refineries (Table 26). The following assumptions were made:

.1 refineries produce, on average, 4.5 units of

wastewater per unit of refining capacity, as

shown by CONCAWE (1994) and EDF (

Epstein et al.1995) studies;

.2 effluents contain 5 ppm to 25 ppm of oil,

depending on the condition and operating

practices of the refineries; and

.3 refineries operate all year round.

226 Based on these assumptions, the estimated maximum total annual input of oil into the

marine environment from refineries would be approximately 180,000 tonnes of oil per year. The actual

number could be as low as one-quarter to one-half

of this amount if the less efficient refineries were

actually releasing less than 25 ppm of oil in their

effluents and were operating on a less than full-time

schedule. The best estimate is, therefore, 45,000-

180,000 tonnes/yr. A median value for oil inputs

from refineries would be 112,500 tonnes/yr, or

113,000 tonnes/yr.

5.1.2 Accidental releases from coastal facilities

227 Figure 44 shows the estimated annual

number of oil spills and amounts of oil spilled into

the marine environment from accidental releases

from coastal facilities. The spill number appears to

have decreased over the last decade, while the spill

amount has stayed fairly constant over the last three

decades, with the notable exceptions of the years

1978, 1981, and 1991. The average annual input is

2,400 tonnes/yr.

228 Notable facility oil spills include: the

1974 spill of 39,500 tonnes from the Mizushima

Refinery in Kurashiki, Japan; a 1978 spill of 11,430

tonnes after an explosion in a Texaco storage facility

in Los Angeles, California, USA; an earthquake-related spill of 60,200 tonnes from a Tohoku Oil facility in

Sendai, Japan, in 1978; a spill of 21,430 tonnes of oil

from a storage depot in Beira, Mozambique in 1979;

a 1980 spill of 10,714 tonnes from a Petroleos

Mexicanos facility in Coatzacoalcos, Mexico; a spill

of 106,000 tonnes from a Kuwait Oil terminal in

Shuybah, Kuwait, in 1981; a spill of 11,565 tonnes

from a Texaco tank farm in Newark, New Jersey, USA

in 1983; and a spill of 34,286 tonnes from the

Refineria Las Minas in Colon, Panama, in 1986.

229 War-related incidents involving coastal

facilities are included in estimates of overall warrelated spillage. This is particularly important in relation to estimates of inputs into the Arabian (Persian)

Gulf, given the hostilities of 1991 and 2003.

5.2 Reception facilities

230 Oily waste that is generated onboard

ships has often been regarded as “waste” for disposal. It is the oil from all of the sources identified in

Sections 3.1 and 3.2 – from oil recovered from ballast water, to oil in machinery spaces aboard tankers

and non-tankers, to fuel oil sludge.

231 Reception facilities exist in many countries, intended for the receipt of these oily wastes

(IMO 2000; Intertanko 1996a; 1997; 1998b). A variety of separating techniques for oily waste are in use

at reception facilities; these include filtration, centrifuges, flotation and separation from water in large

settling tanks and ponds (Intertanko 1996a; 1998b).

Disposal techniques for oily waste at the facilities

include landfill, sludge farming and incineration.

However, there is also wastewater that after filtering

should contain no more than 5 ppm oil. Such treated wastewater will be discharged into the sea.

5 OTHER INPUTS OF OIL INTO THE SEA FROM SEA-BASED

ACTIVITIES AND RELATED TOPICS 
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 49

Table 26. Estimated Maximum Coastal Oil Refinery Effluent Output1 Regional Estimates (1988-1997)

(Source: Etkin, Environmental Research Consulting)

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Region Daily Crude Capacity2 Output3 Discharge in Effluent3

Number Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

1 2,562,900 bpd 168,943,805,200 gal 844,662 gal

366,129 tpd 639,454,221 m32,873 t

2 743,920 bpd 49,038,462,400 gal 1,225,980 gal

106,274 tpd 185,611,137 m34170 t

3 2,236,665 bpd 153,371,430,200 gal 766,752 gal

3189,524 tpd 580,512,605 m32,608 t

4 11,174,650 bpd 736,621,753,400 gal 8,891,442 gal

1,596,379 tpd 2,788,121,701 m330,243 t

5 2,140,505 bpd 141,254,292,200 gal 3,527,412 gal

305,786 tpd 534,064,910 m311,998 t

6 1,651,328 bpd 108,853,890,300 gal 2,647,470 gal

235,904 tpd 412,013,211 m39,005 t

7 4,557,840 bpd 300,448,255,100 gal 1,502,046 gal

651,120 tpd 1,137,200,057 m35,109 t

8 1,227,100 bpd 80,889,204,890 gal 1,4458,534 gal

175,300 tpd 306,166,559 m34,961 t

9 7,624,289 bpd 502,585,506,800 gal 6,641,166 gal

1,089,184 tpd 1,902,291,850 m322,589 t

10 1,644,380 bpd 108,395,885,100 gal 2,709,798 gal

234,911 tpd 410,279,656 m39,217 t

11 695,550 bpd 45,849,960,470 gal 1,146,306 gal

94,221 tpd 173,542,621 m33,899 t

12 4,560,500 bpd 28,345,169,920 gal 142,002 gal

651,500 tpd 107,286,790 m3483 t

13 123,350 bpd 8,131,108,764 gal 203,154 gal

17,621 tpd 30,776,339 m3691 t

14 581,853 bpd 38,355,167,890 gal 958,734 gal

83,122 tpd 145,174,746 m33,261 t

15 4,213,800 bpd 277,769,482,100 gal 6,943,986 gal

601,971 tpd 1,051,360,644 m323,619 t

16 1,616,052 bpd 106,528,531,900 gal 2,663,052 gal

230,865 tpd 403,211,703 m39,058 t

17 10,891,400 bpd 717,950,196,700 gal 12,054,294 gal

1,555,914 tpd 2,717,449,647 m341,001 t

18 782,300 bpd 51,568,433,670 gal 368,970 gal

111,757 tpd 195,187,107 m31,255 t

1Estimates represent maximum values based on assumptions that refineries operate at full capacity year-round, effluents are 5 ppm or 25 ppm oil depending on national laws and practices, and refineries produce 4.5 units of wastewater per unit refining capacity; actual discharges may be as low as 25-50%

of these amounts if refineries on less than full-time schedule.

2Figures derived from PennWell Oil Directories.

3Estimates based on independent study by Etkin (1999) using assumptions above; CONCAWE Report 3/94 Trends in Oil Discharged With Aqueous

Effluents from Oil Refineries in Western Europe – 1993 Survey; Environmental Defense Fund (Epstein, L. , S. Greetham, and A. Karuba) 1995, Ranking

Refineries.
50 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Table 27. Estimated Maximum Coastal Oil Refinery Effluent Output National Estimates (1988-1997)

(Source: Etkin, Environmental Research Consulting)

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Country Daily Crude Capacity2 Output3 Discharge in Effluent3

Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

Albania 40,000 bpd 2,636,760,121 gal 65,915 gal

5,714 tpd 9,980,167 m3224.20 t

Algeria 530,000 bpd 34,937,070,089 gal 873,389 gal

75,714 tpd 132,237,207 m32,970.71 t

Angola 32,100 bpd 2,115,999,993 gal 52,896 gal

4,586 tpd 8,009,084 m3179.92 t

Argentina 709,485 bpd 46,768,541,596 gal 1,169,162 gal

101,355 tpd 177,019,461 m33,976.74 t

Australia 698,000 bpd 46,011,461,965 gal 230,058 gal

99,714 tpd 174,153,906 m3782.51 t

Bahrain 243,000 bpd 16,018,317,070 gal 400,440 gal

34,714 tpd 60,629,512 m31,362.04 t

Bangladesh 31,200 bpd 2,056,673,826 gal 51,415 gal

4,457 tpd 7,784,530 m3174.88 t

Barbados 3,000 bpd 197,756,870 gal 4,945 gal

429 tpd 748,512 m316.82 t

Belgium 607,000 bpd 40,012,832,933 gal 200,064 gal

86,714 tpd 151,449,027 m3680.49 t

Brazil 1,402,520 bpd 92,452,715,772 gal 2,311,216 gal

200,360 tpd 349,934,579 m37,861.28 t

Brunei 8,500 bpd 560,311,397 gal 14,006 gal

1,214 tpd 2,120,785 m347.64 t

Bulgaria 300,000 bpd 19,775,699,986 gal 494,370 gal

42,857 tpd 74,851,249 m31,681.53 t

Cameroon 42,000 bpd 2,768,598,035 gal 69,211 gal

6,000 tpd 10,479,175 m3235.41 t

Canada 778,900 bpd 51,344,309,111 gal 256,721 gal

111,271 tpd 194,338,793 m3873.20 t

Chile 143,700 bpd 9,472,560,222 gal 236,802 gal

20,529 tpd 35,853,748 m3805.45 t

China 2,200,000 bpd 145,021,800,072 gal 3,625,385 gal

314,286 tpd 548,909,160 m312,331.24 t

Columbia 264,400 bpd 17,428,983,644 gal 435,705 gal

37,771 tpd 65,968,901 m31,481.99 t

Congo 21,000 bpd 1,384,298,885 gal 34,607 gal

3,000 tpd 5,239,587 m3117.71 t

Costa Rica 15,000 bpd 988,784,880 gal 24,720 gal

2,143 tpd 3,742,562 m384.08 t

Croatia 143,472 bpd 9,457,530,676 gal 236,429 gal

20,496 tpd 35,796,861 m3804.18 t

Cyprus 18,600 bpd 1,226,093,283 gal 30,652 gal

2,657 tpd 4,640,777 m3104.26 t

Denmark 183,500 bpd 12,096,136,499 gal 60,482 gal

26,214 tpd 45,784,014 m3205.72 t
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 51

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Country Daily Crude Capacity2 Output3 Discharge in Effluent3

Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

Dom. Rep. 48,000 bpd 3,164,112,040 gal 79,101 gal

6,857 tpd 11,976,200 m3269.05 t

Ecuador 147,000 bpd 9,690,092,990 gal 242,241 gal

21,000 tpd 36,677,112 m3823.95 t

Egypt 532,153 bpd 35,078,993,574 gal 876,937 gal

76,022 tpd 132,774,389 m32,982.78 t

El Salvador 15,100 bpd 995,376,935 gal 24,884 gal

2,157 tpd 3,767,513 m384.64 t

Ethiopia 18,000 bpd 1,186,542,015 gal 29,662 gal

2,571 tpd 4,491,075 m3100.89 t

Finland 200,000 bpd 13,183,800,079 gal 329,580 gal

28,571 tpd 49,900,833 m31,121.02 t

France 1,851,430 bpd 122,044,414,315 gal 610,223 gal

264,490 tpd 461,939,494 m32,075.59 t

Gabon 24,000 bpd 1,582,056,020 gal 39,549 gal

3,429 tpd 5,988,100 m3134.52 t

Germany 409,000 bpd 26,960,871,033 gal 134,805 gal

58,429 tpd 102,047,203 m3458.52 t

Ghana 26,600 bpd 1,753,445,466 gal 43,835 gal

3,800 tpd 6,636,811 m3149.10 t

Greece 395,500 bpd 26,070,964,587 gal 651,745 gal

56,500 tpd 98,678,897 m32,216.82 t

Guatemala 16,000 bpd 1,054,704,101 gal 26,366 gal

2,286 tpd 3,992,067 m389.68 t

Honduras 14,000 bpd 922,865,924 gal 23,070 gal

2,000 tpd 3,493,058 m378.47 t

India 1,046,827 bpd 69,005,789,019 gal 1,725,069 gal

149,547 tpd 261,187,695 m35,867.58 t

Indonesia 860,200 bpd 56,703,523,944 gal 1,417,527 gal

122,886 tpd 214,623,482 m34,821.52 t

Iran 1,089,300 bpd 71,805,566,617 gal 1,795,061 gal

155,614 tpd 271,784,885 m36,105.65 t

Iraq 318,500 bpd 20,995,210,479 gal 524,858 gal

45,500 tpd 79,467,076 m31,785.23 t

Ireland 56,000 bpd 3,691,463,959 gal 18,457 gal

8,000 tpd 13,972,233 m362.78 t

Israel 221,000 bpd 14,568,098,964 gal 72,841 gal

31,571 tpd 55,140,420 m3247.76 t

Italy 2,420,358 bpd 159,547,578,952 gal 797,737 gal

345,765 tpd 603,889,398 m32,713.39 t

Jamaica 32,000 bpd 2,109,407,939 gal 52,732 gal

4,571 tpd 7,984,133 m3179.36 t

Japan 4,470,650 bpd 294,700,777,454 gal 1,473,504 gal

638,664 tpd 1,115,445,789 m35,011.92 t

Kenya 90,000 bpd 5,932,709,811 gal 148,311 gal

12,857 tpd 22,455,374 m3504.46 t

Table 27. (cont'd)
52 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Country Daily Crude Capacity2 Output3 Discharge in Effluent3

Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

Korea, N. 42,000 bpd 2,768,598,035 gal 69,211 gal

6,000 tpd 10,479,175 m3235.41 t

Korea, S. 1,147,100 bpd 75,615,684,909 gal 1,890,308 gal

163,871 tpd 286,206,226 m3 6,429.62 t

Kuwait 368,000 bpd 24,258,191,954 gal 606,428 gal

52,571 tpd 91,817,532 m3 2,062.68 t

Lebanon 37,500 bpd 2,471,962,465 gal 61,796 gal

5,357 tpd 9,356,406 m3 210.19 t

Liberia 15,000 bpd 988,874,880 gal 24,720 gal

2,143 tpd 3,742,562 m3 84.08 t

Libya 348,400 bpd 22,966,179,714 gal 574,129 gal

49,771 tpd 86,927,251 m3 1,952.82 t

Lithuania 266,600 bpd 17,547,005,402 gal 439,330 gal

38,086 tpd 66,517,810 m3 1,494.32 t

Madagascar 16,350 bpd 1,077,775,631 gal 26,942 gal

2,336 tpd 4,079,393 m3 91.64 t

Malaysia 263,000 bpd 17,336,696,999 gal 433,397 gal

37,571 tpd 65,619,595 m3 1,474.14 t

Martinique 16,000 bpd 1,054,704,101 gal 26,366 gal

2,286 tpd 3,992,067 m3 89.68 t

Mexico 1,524,000 bpd 100,460,555,949 gal 2,511,404 gal

217,714 tpd 380,244,345 m3 8,542.19 t

Morocco 154,600 bpd 10,191,077,485 gal 254,766 gal

22,086 tpd 38,573,344 m3 866.55 t

Myanmar 32,000 bpd 2,109,407,939 gal 52,732 gal

4,572 tpd 7,984,133 m3 179.36 t

Netherlands 1,230,500 bpd 81,113,329,447 gal 405,567 gal

175,786 tpd 307,014,873 m3 1,379.48 t

Neth. Antilles 470,000 bpd 30,981,930,039 gal 774,514 gal

67,143 tpd 117,266,957 m3 2,634.40 t

New Zealand 84,300 bpd 5,556,971,704 gal 27,786 gal

12,043 tpd 21,033,201 m3 94.51 t

Nicaragua 16,000 bpd 1,054,704,101 gal 26,366 gal

2,286 tpd 3,992,067 m3 89.68 t

Nigeria 433,250 bpd 28,559,406,792 gal 713,953 gal

61,893 tpd 108,097,679 m3 2,428.41 t

Norway 285,200 bpd 18,800,098,685 gal 94,001 gal

40,743 tpd 71,158,587 m3 319.73 t

Oman 80,000 bpd 5,273,519,979 gal 131,833 gal

11,429 tpd 19,960,333 m3 448.41 t

Pakistan 120,975 bpd 7,974,550,977 gal 199,356 gal

17,282 tpd 30,183,766 m3 678.08 t

Panama 100,000 bpd 6,591,899,907 gal 164,790 gal

14,286 tpd 24,950,416 m3 560.51 t

Peru 188,820 bpd 12,446,825,539 gal 311,158 gal

26,974 tpd 47,111,376 m3 1,058.36 t

Table 27. (cont'd)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 53

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Country Daily Crude Capacity2 Output3 Discharge in Effluent3

Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

Philippines 278,450 bpd 18,335,145,463 gal 458,858 gal

39,779 tpd 69,474,434 m31,560.74 t

Poland 333,000 bpd 21,951,026,881 gal 548,751 gal

47,571 tpd 83,084,886 m31,866.50 t

Portugal 294,000 bpd 19,380,185,981 gal 484,483 gal

42,000 tpd 73,354,224 m31,647.90 t

Puerto Rico 127,000 bpd 8,371,713,062 gal 41,860 gal

US 8,143 tpd 31,687,029 m3142.38 t

Qatar 60,000 bpd 3,955,140,050 gal 98,875 gal

8,571 tpd 14,970,250 m3336.31 t

Romania 733,102 bpd 48,325,350,664 gal 1,208,081 gal

104,729 tpd 182,912,001 m34,109.12 t

Russian Fed. 630,800 bpd 41,581,705,109 gal 1,039,496 gal

90,114 tpd 157,387,226 m33,535.70 t

Saudi Arabia 1,862,500 bpd 122,774,137,621 gal 3,069,219 gal

266,071 tpd 464,701,505 m310,439.52 t

Senegal 22,600 bpd 1,489,769,375 gal 37,244 gal

3,229 tpd 5,638,794 m3126.68 t

Sierra Leone 10,000 bpd 659,190,096 gal 16,479 gal

1,429 tpd 2,495,042 m356.05 t

Singapore 1,029,000 bpd 67,830,650,933 gal 1,659,692 gal

147,000 tpd 256,739,784 m35,767.66 t

Slovenia 14,700 bpd 969,009,246 gal 24,226 gal

2,100 tpd 3,667,711 m382.40 t

Somalia 10,000 bpd 659,190,096 gal 16,479 gal

1,429 tpd 2,495,042 m356.05 t

South Africa 430,500 bpd 28,378,129,542 gal 141,890 gal

61,500 tpd 107,411,542 m3482.62 t

Spain 1,301,328 bpd 85,782,240,407 gal 428,911 gal

185,904 tpd 324,686,754 m31,458.88 t

Sri Lanka 50,000 bpd 3,295,949,954 gal 82,396 gal

7,143 tpd 12,475,208 m3280.26 t

Sudan 21,700 bpd 1,430,442,208 gal 35,759 gal

3,100 tpd 5,414,240 m3121.63 t

Sweden 427,500 bpd 28,180,372,526 gal 140,902 gal

61,071 tpd 106,663,030 m3479.26 t

Syria 237,394 bpd 15,648,774,982 gal 391,202 gal

33,913 tpd 59,230,791 m31,330.62 t

Thailand 220,550 bpd 14,538,435,381 gal 363,446 gal

31,506 tpd 55,028,143 m31,236.21 t

Trinidad 246,000 bpd 16,216073,941 gal 405,385 gal

35,143 tpd 61,378,024 m31,378.86 t

Tunisia 34,000 bpd 2,241,246,116 gal 56,028 gal

4,857 tpd 8,483,142 m3190.57 t

Turkey 713,580 bpd 47,038,480,020 gal 1,175,912 gal

101,940 tpd 178,041,181 m33,999.70 t

Table 27. (cont'd)
54 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Coastal Refinery Estimated Annual Effluent Estimated Annual Oil

Country Daily Crude Capacity2 Output3 Discharge in Effluent3

Barrels per day US Gallons US Gallons per year

(Tonnes per day) (m3) (Tonnes per year)

United Arab 192,500 bpd 12,689,407,374 gal 317,220 gal

Emirates 27,500 tpd 48,029,551 m31,078.98 t

United 1,842,640 bpd 121,464,986,198 gal 607,325 gal

Kingdom 263,234 tpd 459,746,352 m3 2,065.73 t

United States 10,606,215 bpd 699,151,086,688 gal 3,495,754 gal

of America 1,515,174 tpd 2,646,294,802 m3 11,890.32 t

Uruguay 28,500 bpd 1,878.691,590 gal 46,967 gal

4,071 tpd 7,110,869 m3 159.75 t

Venezuela 1,167,000 bpd 76,927,473,048 gal 1,923,101 gal

166,714 tpd 291,171,359 m3 6,541.16 t

Virgin I. US 545,000 bpd 35,925,854,970 gal 179,628 gal

77,857 tpd 135,979,769 m3 610.98 t

Yemen 114,500 bpd 7,547,725,573 gal 188,686 gal

16,357 tpd 28,568,227 m3 641.79 t

Yugoslavia 444,233 bpd 29,283,395,109 gal 732,054 gal

63,462 tpd 110,837,983 m3 2,489.98 t

Others 542,500 bpd 35,761,057,578 gal 893,986 gal

77,500 tpd 135,356,009 m3 3,040.77 t

TOTAL 54,893,382 bpd 3,618,516,849,000 US gal 52,786,962

7,841,912 tpd 13,696,127,360 m3 US gal p/yr.

p/yr. 179,547.49 tonnes p/yr.

1Estimates represent maximum values based on assumptions that refineries operate at full capacity year-round, effluents are 5 ppm or 25 ppm oil depending on national laws and practices, and refineries produce 4.5 units of wastewater per unit refining capacity; actual discharges may be as low as 25-50%

of these amounts if refineries on less than full-time schedule.

2Figures derived from PennWell Oil Directories.

3Estimates based on independent study by Etkin1999 using assumptions above; CONCAWE Report 3/94 Trends in Oil Discharged With Aqueous Effluents

from Oil Refineries in Western Europe – 1993 Survey; Environmental Defense Fund, Epstein, L, S. Greetham, and A. Karuba, 1995, Ranking Refineries.

Table 27. (cont'd)

Figure 44. Estimated Annual Oil Spills From Coastal Facilities 1968-1999 (Based on Environmental Research

Consulting Database)
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 55

232 The IMO has data on reported reception

facilities (MEPC 1990; Carpenter and Macgill 2003).

There is no established international standard applicable to discharges from reception facilities. The

Oslo and Paris Commission has agreed on an

OSPAR recommendation for reception facilities with

a throughput above 5 tonnes of oil per year; this limits the oil content in effluents from reception facilities

in North West Europe to 15 mg oil/litre of effluent

(PARCOM Recommendation 87/2).

233 Reception facilities are thought to be a

significant coastal, sea-based, i.e. from ships,

source of oil(s) into the marine environment.

However, no regional or global statistics on oil content and volumes of their discharges were found.

Hence, it is not possible at this time to estimate an

average annual input of oil into the sea from reception facilities worldwide.

5.3 Oil in waste materials dumped at sea

234 The presence of oil in sediments and

dredging spoils from harbours, usually described as

polycyclic aromatic hydrocarbons (PAHs) of all kinds,

is considered to be in such low total quantities as to

not be a significant oil input, for the purposes of this

study (Robert Engler, USA, pers. comm.).

Consideration of this input would best fit under landbased activities, in any event. Such oil inputs are

regulated internationally under the London

Convention, 1972. 

5.4 Fuel dumps from aircraft 

235 Aircraft inputs of oil into the sea were

considered, more to determine the magnitude of this

source than to include it as a ship or other sea-based

activity source. They are almost always overlooked

as a source input of hydrocarbons to the sea. Slicks

formed from aviation fuel could be taken, initially, as

a boat or ship-originating source; chemical analysis

would sort out the origin, but time and resources

might be lost in the investigation.

236 Aircraft sometimes dump aviation fuel

(jet fuels, largely kerosenes) prior to landing. This is

either as part of normal practice to lighten aircraft

weight if a plane has to return to an airport unexpectedly, or in extreme emergencies to reduce risks of

fire and explosion if a disabled aircraft is attempting

to land (e.g. Swiss Air 111, Sept.1998, off Peggy’s

Cove, Nova Scotia, Canada). Such practice is

regarded by operators as an uncommon event

(British Airways 2000a). Dumping may take place

over water bodies if they are close by; this sometimes occurs over the lower Great Lakes (M. Fingas,

pers. comm. to D. Etkin). Selection of a dumpsite

over water theoretically minimizes the potential hazards to humans. There apparently are no accurate

collated statistics publicly available regarding the

frequency of fuel dumps, site locations and quantities on a global basis. Military aircraft in the United

States were required to report non-combat fuel jettisoning events between 1973 and 1978 as part of a

study conducted over 3? years. This study reported

some 1000 jettisoning incidents per year for the US

Air Force as a whole (Clewell, 1980). In addition, discharges of unburned fuel are possible as a result of

design/operational characteristics of individual

engines, generally in vapour form. For example, one

airline operating a fleet of some 277 aircraft reported

losses of unburned hydrocarbons of 3,100 tonnes

per annum for the period 1999-2000 (British Airways

2000a & b).

237 Released fuel is likely to evaporate to

some degree and, therefore, not reach the earth’s

surface. Also, weather conditions and fuel type will

likely influence deposited quantities (see: Clewell,

1983; Good & Clewell 1979). In an evaluation of the

potential hazard of fuel jettisoning, the US Agency

for Toxic Substances and Disease Registry (ATSDR

1999) considered that more than 98% of fuel

released at an altitude of 1,500m and at above freezing temperatures would evaporate before reaching

the ground. Moreover, at warmer temperatures, no

liquid fuel was detected on the ground when fuel had

been released at 750m altitude. 

238 Hence, although fuel jettisoning by aircraft is a recognized hydrocarbon-oil source input to

the sea (though not usually considered a sea-based

activity), the lack of collated statistics means that

estimates of input amounts are not available or possible to calculate accurately. For this reason and the

presumed infrequency of the events, this activity is

considered unlikely to constitute a significant input

of oil to the oceans.

5.5 Small craft activity

5.5.1 Outboard engines

239 Small, predominantly leisure, craft19 are

significant users of fuel oils and lubricants. They are

a potentially important source of oil and hydrocarbons into the sea. While it is anticipated that large

spills of outboard fuels are comparatively rare and

will have been captured in existing statistics, it is

probable that hydrocarbons will be lost during refuelling and fuel transfer activities. Over-priming and

choking of outboard engines by inexperienced or

incompetent operators can also lead to losses of fuel

from carburettors and of lubricating oils to marine

waters. While these losses are comparatively minor,

the very large number of outboard engines globally

means that they are collectively of significance.

Based upon the analysis of tricyclic terpanes, contamination of sediments and biota with outboard

lubricating oils could be clearly differentiated from

automotive lubricants in a Canadian study, testifying

to the potential significance of these inputs and the

interest in monitoring such contamination (Bieger et

al. 1996).

18 For the purposes of this study, small craft are those operating on either 2 or 4-stroke engines. In the context of regulating organotin-containing marine paints, previously used on

small boats, small craft are those 25 m or under, in length, at

the waterline.
56 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

240 The use of outboard engines, the design

of which changed little in the past 50 years until very

recently (NRC 2003), is known to introduce oil

derived hydrocarbons to the waters in which they

operate (Wachs et al. 1992; Wachs & Wagner 1990;

Juttner et al. 1995). These derive both from partially

combusted fuels and from lubricants. Outboard

motors operating on a two-stroke cycle have been

particularly studied and in many cases these engines

introduce the exhaust directly below the water surface. One early study (Coates & Lassanske 1990)

based upon a notional average duty cycle and conducted by outboard motor manufacturers suggested

that a 70-horsepower two-stroke engine would emit

1.5kg of hydrocarbons per hour of use, comprising

around 8.3% of the fuel/lubricant mix consumed (19-

23 litres or 5-6 US gallons per hour). Subsequently,

published data (USEPA 1991) showing substantially

higher hydrocarbon emissions from two-stroke outboard motors of the order of 25-30% of the fuel consumed and these engines are considered to be the

second largest average non-road engine contributors to national emissions of hydrocarbons, emitting

some 30% of the total (see USEPA 1996). Very

recently, however, i.e. in the past 5 years (NRC

2003), manufacturers claim a reduction in emissions

of 50-80% from outboard motors (Walker, pers.

comm.), a fact not considered in the calculations

below.

241 Other figures reported in the literature for

smaller engines (10 horsepower) indicate that

between 205-483g of unburned hydrocarbons are

emitted per litre of fuel consumed. This is dependent upon design and operating characteristics (see:

Wachs et al. 1992; Wachs & Wagner 1990). These

figures are consistent with those derived by the

USEPA (1991). One of the first estimates produced

of the significance of outboard engine emissions

drew on the estimates of Coates and Lassanske

(1990) to produce a lower bound value and a higher

bound value was derived according to USEPA (1991)

with a number of additional assumptions (Mele

1993). 

242 Mele (1993) assumed that a 70 horsepower outboard (considered a typically sized engine)

emits around 8.3% of the fuel and lubricant mix consumed as a lower bound, and as an upper bound

emits 25% of the mix at a 20% flat throttle setting.

Further, it was assumed that 8 million recreational

craft, two-thirds of the total registered in the US,

make 80 million trips annually and that each trip consumes an average of 20 US gallons a trip (i.e. 10 trips

per boat annually of around 4 hours duration). Thus,

the annual outboard motor fuel consumption in this

sector can be estimated at 1.6 billion gallons. These

assumptions appear to be reasonable. This translates to a total hydrocarbon emission into air and

water of between 133 and 400 million gallons annually. If it is assumed that one gallon equates to 2.81

kilos, this translates to emissions of between

374,818 (~375,000) tonnes and 1,127,272

(~1,100,000) tonnes of hydrocarbons per annum into

air and water in the US alone. It was estimated

based on a 1980 study that there are 800,000 outboard engines in use in Canada (see: Warrington,

1999). Making the same assumptions applied to the

US situation, a range of between 37,481 (~37,000)

and 112,272 (~112,000) tonnes of hydrocarbons are

emitted into air and water by such engines in Canada

annually.

243 Estimates of the US emissions can be

arrived at in an alternative manner using figures provided by the USEPA (1991). This report estimates

that typical annual operation of between 74-142

boats with outboard engines will generate 10 tonnes

per annum of hydrocarbons into air and water. On

the basis of the eight million boats existing in the US

of this type, this translates to between 563,380

tonnes and 1.081 million tonnes annually into air and

water, of the same order of magnitude as the estimates made by Mele (1993). 

244 Considerable uncertainties exist in the

above estimates, in addition to those introduced by

assuming operation patterns and fuel consumption

and annual usage. They arise from the fact that differences in emissions can result from the use of synthetic as opposed to mineral oil lubricants (see

Wachs et al. 1992) and from the substitution of normal gasoline with other fuels such as alkylate-based

petrol/gasoline (see: Ostermark & Petersson, 1993).

In addition, the use of MTBE may also modify the

emission profile (Gabele & Pyle 2000). Finally, the

above estimates make no allowance for particulates

emitted and the hydrocarbons (particularly PAH)

associated with these (see Kado et al. 2000), nor the

relative proportions of hydrocarbons entering air and

water, respectively. 

5.5.2 Inboard engines

245 Four stroke engines comprise a small

proportion of outboard engines but inboard and

stern drive engines are mainly of this type. These

engines, which burn gasoline/petrol, emit a wide

variety of hydrocarbons (aromatic hydrocarbons and

aldehydes, as analysed in water) in the exhaust

(Juttner, 1994; Kado et al. 2000). However, the

design and operational characteristics of the inboard

engines mean that combustion efficiency is greater

and lubricant losses are significantly less than with

outboard engines (USEPA 1991; 2000). Many

inboard engines emit exhaust above the water surface but often through a port carrying the engine

cooling water as well. Diesel marine engines, in

common with their counterparts in terrestrial use and

in common use in many countries, will likely emit

similar hydrocarbons (no analysis was found of such

emissions to water), although such engines are primarily of concern due to their particulate emissions

(USEPA 1999).

246 For the US, Mele (1993) made the

assumption that 4 million US leisure water craft are

powered by stern-drive/inboard engines and that the

additional fuel consumption amounts to 0.8 billion

gallons per year. Assuming that emissions of hydro-
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 57

carbons are a maximum of 8.3% of hydrocarbons

consumed (the lower bound estimated for two-stroke

motors), this accounts for an additional 187,127

(~187,000) tonnes of hydrocarbon inputs, to air and

water, per year from leisure craft in the US. This is

probably an extreme scenario. It is generally considered that the emissions from 4-stroke engines are an

order of magnitude less than those from a 2-stroke

engine of equivalent power (USEPA 1991; Juttner et

al. 1995). Assuming, emissions of around 2.5% of

fuel consumption, this implies 56,363 (~56,000)

tonnes of hydrocarbons per year in the US entering

the air and water from leisure water craft.

5.5.3 Small craft activity: Overview 

247 Estimates of hydrocarbon emissions to

the air and aquatic environments in the US of up to

1.12 million tonnes annually from 2-stroke marine

engines (Range 374,818-1.12 million tonnes) and

around 187,000 tonnes (Range 56,363-187,127

tonnes) from four stroke inboard engines represent a

maximum input, due to fate of introduced hydrocarbons and the partitioning between air and water not

being quantified. Sources of potential uncertainty in

the estimates include:

.1 average usage and engine load factors may

be subject to considerable variation on a

local and seasonal basis;

.2 hydrocarbons emitted through engine

exhaust, even below the water surface as is

the case with most outboard engines, are

likely to be only partially retained in the water

column since some components are highly

volatile. It is necessary to determine the relative proportions of hydrocarbons staying in

the water and entering the air and staying

airborne, in order to make exact estimates of

the hydrocarbon contribution to the water

column;

.3 it has been assumed that all outboard

engines are of the 2-stroke type, whereas

some (albeit a minority) operate on a 4-

stroke cycle;

.4 not all engines are operated in the marine

environment, and some will operate in environments with no direct connection with the

sea;

.5 the assumption is that all engines are on

average 70 horsepower, whereas some are

of greater and some of lesser power. No

breakdown of this is currently available; and

.6. no consideration has been made of commercial engine emissions.

248 It is not clear to what extent the small

craft input estimates have relevance to other areas of

the world. While small (leisure) craft are also numerous in other countries, no statistical breakdown with

precise numbers appears to be available for countries outside the US and Canada. Assuming, conservatively, that the US has at least 10% of the global

total of 2-stroke outboard motors, this leads to a

global emission of hydrocarbons, to the air and

water of aquatic environments, of 3.7-11.2 million

tonnes annually. On the same basis, 4-stroke motors

would emit in the range of 0.58-1.87 million tonnes of

hydrocarbons. Totalling the top and bottom of each

range leads to an estimate of 4.28-13.7 million

tonnes, or 4.3-13.7 million tonnes of hydrocarbon

emissions per year, to the air and aquatic environments.

249 It was not possible in our study to estimate the impact upon the above estimates of the

fate of these hydrocarbons, nor the proportion emitted to marine waters as opposed to freshwater systems, nor the relative proportion in air versus water.

It has simply been assumed that since these hydrocarbons are mostly introduced directly into the water

from the exhaust, they represent de facto an input. If

it is assumed that fully half of these emissions take

place directly to marine waters, then a final (imprecise) estimate of inputs is between 2.14-5.6, or a

median of 3.9 million tonnes/yr. Notwithstanding

any imprecision in these estimates, it can be surmized that if the US situation is representative, then

small marine engines, particularly those operating on

a 2-stroke cycle, constitute a highly significant

potential input of oil derived hydrocarbons to the

marine environment on a global basis. 

250 The NRC (2003) study developed an

equation for loading estimates from recreational

craft, based on the function of two-stroke engines,

and considering the aromatic hydrocarbons that

enter the water. Annual input estimates from twostroke engines are “between 2,100 and 8,500 tonnes

(average 5,300 tonnes) per year for coastal waters of

the United States”. Conservatively, if one adopts that

estimate and it represents 10% of global total input

from two-stroke engines (see above), a second estimate of annual input of oil from small leisure craft

would be 10 x 5,300 tonnes or 53,000 tonnes/yr.

251 Awareness of the significance of outboard and personal watercraft engines in relation to

both air and water quality has resulted in legislation

to bring these emissions under control. It is mandated in the US that all manufacturers must produce

engines with 75% lower emissions by 2006 (see

USEPA 2000). The precise impact of the regulations,

staged over a period that began in 1998, will depend

in part upon the degree to which older engines continue in use. 

5.6 Natural oil seeps

252 Major inputs of oil into the sea occur

from natural oil seeps in the seabed and oil entering

from erosional processes in coastal land. Natural

seeps contribute a major fraction; minor contributions are from erosional processes. Seeps were

reviewed in NRC (1985, 2003) and in detail by Boehm
58 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

et al. (2000), Brown et al. (1996), Kvenvolden and

Harbaugh (1983), MacDonald (1998), and Page et al.

(1998).

253 The seepage of an area, i.e. the number

of seeps per unit area and the rate for each seep,

relates to its geological structure and the volume of

associated sediment basins. Seeps are associated

with regions of high tectonic activity, clustered within the continental margins where the thickness of

sedimentary rocks that provide the needed source

rocks for the seepage, exceeds a certain minimum.

Thus, natural seeps occur along the Pacific Rim e.g.

common in Alaskan waters, in central North America,

in the Gulf of Mexico, in the eastern Arctic and

around the Mediterranean Sea. These are known

seeps, but it seems that many have not yet been discovered.

254 Oil seepage rates have been calculated,

taking into account estimated oil deposits available

for seepage within a reasonable geological time

frame. Wilson et al. (1973a,b) made an estimate of

0.6 million tonnes/yr. The NRC Committee of 1975

made estimates of 0.2-6 million tonnes/yr. (NRC

1975). The NRC Committee on oil pollution, working

from 1981-85, estimated that the average rate of oil

seepage over time ranged from 0.02 to 2.0 million

tonnes/yr., with a best estimate of 0.25 million

tonnes/yr. (NRC 1985). Most recently, the NRC oil

committee using the 1985 approach has determined

the best estimate to be 600,000 tonnes/yr. (NRC

2003; Kvenvolden 2004, pers.comm.), the same as

Wilson’s and NRC (1975) estimates, with a range of

0.2-2 million tonnes/yr. The estimate of oil entering

the oceans each year from natural seeps may well

increase as more seeps are discovered, particularly

in Polar (Arctic, Antarctic) regions. The potential

area of continental margins and oceanic spreading

axes (see Kvenvolden and Simoneit 1990) where

sub-marine seeps occur or may occur is vast, making a global inventory of seep inputs difficult with

accuracy.

255 Crude oil entering the sea from natural

seeps can be readily distinguished from other crude

oils, as well as from other oil and hydrocarbon

sources; qualitatively, it is also possible to distinguish sea-based sources of hydrocarbons from natural sources such as seeps and forest fires (Page et

al. 1998). This is important not only for developing

the overall oil input budgets, but also for determining

the origin of tar in the ocean (pelagic and littoral) and

quantitatively assessing its significance as an indicator of ship-based pollution (see Section 5.8 below).

5.7 Rocket launches

256 Rocket launches, though also not technically a sea-based source or activity, have the

potential to introduce oil to the marine environment

as a result of the release of unburnt propellant. No

collated statistics exist but some data exist for individual projects. The environmental impact assessment of the “Sea launch” system which uses

kerosene as a propellant, and which is designed to

be launched from an offshore platform, suggests that

stage 1 of this vehicle will contain some 2000kg of

unused kerosene while stage 2 contains a residual

450 kg of this hydrocarbon propellant (ICF Kaiser,

1999).

257 While the second stage is expected to

rupture or break up after separation from the main

vehicle, this is only regarded as a possibility in the

case of the first stage. Hence, while the residual

contents of the second stage may be expected to

evaporate high in the atmosphere (above 160km) in

the case of the first stage, all or part of the residual

kerosene may be expected to fall into the ocean after

this stage separates at a height of 60km. The

assessment (ICF Kaiser, 1999) predicts that any

kerosene reaching the sea surface could be expected to form a slick covering several square kilometres.

Given the volatile nature of kerosene, it is likely that

the bulk will evaporate from the sea surface within a

few hours and the hydrocarbons subsequently will

degrade in the atmosphere.

258 Clearly, the actual tonnage of kerosene

reaching the sea is dependent upon the number of

launches and to what degree the detached stage

maintains structural integrity after separation until

impact in the sea. Projections indicate that some six

launches per year are planned. Hence, potentially

some 12 tonnes of kerosene could reach the sea surface annually. In the case of aborted launches, the

quantities could be greater. The Sea Launch system

at point of launch contains 89.7 tonnes of kerosene

in the first stage, 22.9 tonnes in the second and 4.3

tonnes in the final stage. An aborted launch could

cause all or part of this to enter the marine environment. In the industry, overall, there are no figures to

indicate to what extent inputs of hydrocarbon propellant from rocket launches might be expected on a

global basis. Hence, no input values are considered

in this report in the context of ships and sea-based

activities.

5.8 Tar distributions and their

significance regarding inputs from

ships

259 GESAMP’s 1993 review of marine oil pollution as a global problem showed the ubiquitous

nature of oiling and tarring of the world’s beaches

and coastlines (GESAMP 1993, p. 27-35). That

review brought renewed attention to the potential

impacts of oil inputs from ship-based activities, and

concern about the regulatory effectiveness of MARPOL 73/78 and specific national legislation.

260 There is considerable information on the

occurrence and quantities of tar on the world’s seas

and beaches (NRC 1985; GESAMP 1993; Butler et al.

1998). There are many tarred beaches around the

world, from the Mediterranean to South East Asian

seas. This oil is both weathered crude and refined

heavy fuel product. It is highly persistent and in

warmer locations contributes dissolved compounds
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 59

over time to the surrounding water and habitats.

Often tar that reaches a shoreline is covered and

uncovered in the annual cycles of the beaches, complicating monitoring programmes and data interpretation. Tar lumps and tar-sand patties can be buried

in the sand of the supra-littoral zone of a coastline,

probably for years (Butler and Wells, personal observations, Bermuda).

261 Tar reflects both natural and anthropogenic oil inputs. For example, in the Gulf of

Mexico, tar is found along coastlines close to natural

seep areas, which are very abundant in the Gulf

(MacDonald 1998; also see Section 5.6). In contrast,

in Bermuda, beach tar appears to reflect tanker ballast water discharges to the North Atlantic (Butler

1975; Butler et al. 1973, 1998), and may be showing

an improvement, i.e. a reduction, in oil inputs from

tankers plying the eastern North and mid-Atlantic as

the oiling of Bermuda beaches has significantly

declined in recent years (Butler et al. 1998; pers.

observations and unpubl. data, BBSR).

262 Annual quantities of tar per coastline and

per region are impossible to calculate globally with

any accuracy, at this time, notwithstanding the large

literature and considerable international interest in

this topic (see Bibliography). For most locations,

Bermuda perhaps being an exception, tar data are

important primarily as a qualitative indicator of oil

contamination, not as a quantitative indicator reflecting quantities entering the ocean. In this study, such

inputs may be represented already in other discharge

figures (Sections 3 and 4 above). The information on

tar quantities, therefore, was not used in the overall

oil inputs summary (Section 6).

5.9 Oil inputs from unidentified point

sources

263 Oil inputs from unidentified point

sources include vessel spills (illegal discharges),

pipeline spills (leaks undetected by pressure meters

or other pipeline technology), or unmapped natural

seeps. This input is variable and unpredictable. 

264 Figure 45 shows estimates on oil spills

from unidentified point sources into the marine environment. Such spills generally involve a minor number of spills each year and, assuming the source is

ships or pipelines, add a small amount of oil into the

calculation for the total accidental input each year.

265 A notable exception was in 1980. Two

large spills - one of 2,572 tonnes and one of 2,857

tonnes - in the Persian Gulf off Bahrain were reported and attributed to spills from “unidentifiable

sources.” The spills were probably caused by war

actions. Identity of the sources, whether tankers or

oil facilities of some sort, was never verified by officials in the region.

266 The best estimate of oil input into the

sea from unidentified point sources, during the years

1988-1997, is 200 tonnes/yr.
60 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

6.1 Summary

267 This section summarizes the above oil

input sources, rationalizes the assignment and interpretive value of an average annual input figure for oil

into the marine environment, and makes recommendations for future work.

268This study clearly shows the wide range of

types and quantities of oil inputs from ship and seabased activities, as well as the spatial and temporal

variability of accidental spills globally.

269The estimated average annual inputs of oil

into the sea, in tonnes per year for ships and other

sea-based activities, based on the most recent 10

year-period of data available (1988-97) and the most

recent published information, are shown in Table 28.

Figure 45.

Annual Amount of Oil Spilled From Unknown

Sources 1968-1999 (Based on Environmental

Research Consulting Database)

6 SUMMARY AND CONCLUSIONS 

Table 28. Estimated Average Annual Inputs of Oil, in Metric Tonnes per Year (tonnes/yr. or t/yr.), into the Sea

from Ships and Other Sea-based Activities. Data for accidents covered the 1988-97 period. Data are either

calculated or measured. Large uncertainties of estimates are shown in brackets.

(1) Ships - Discharges Ranges(t/y) Est.or Avg.(t/y) 

Operational discharges

Machinery space bilge oil 1,880

Fuel oil sludge 186,120

Oily ballast (fuel tanks) 907

Operational - cargo-related

Tank washing + oil in ballast 19,250

VOC emissions-tankers 250-68,000 68,000

Accidents

Tankers/barges 46,000-256,000 157,900

Non-tankers 5,300

- Sunken ships (casualties) [not possible to estimate]

- Dry docking 2,900

- Scrapping/recycling of ships 14,830

Subtotal (~ 457,000)

(2) Offshore E&P Operational 16,350

Accidents 600

Pipelines 2,800

Subtotal 19,750

(3) Coastal Facilities Coastal refineries 45,000-180,000 112,500

Accidents 2,400

Subtotal 114,900

(4) Other Inputs

(4.1) Reception facilities no data

(4.2) Small craft activity 2.14-5.6 x 106

3.9x106

OR using NRC (2003) methods 53,000

(4.3) Natural Seeps 0.02 – 2.0 x 106 600,000

(4.4) Other sources (unknown) 200

Subtotal > 653,200

Totals – ships (1) ........................................................................................................................................457,000

- ships (1) plus offshore (2)........................................................................................................................477,000

- ships (1) plus offshore (2) plus coastal facilities (3) .................................................................................592,000

- small craft activity ......................................................................................................................................53,000

- natural oil seeps ......................................................................................................................................600,000

- GRAND TOTAL (minus oil seeps) ............................................................................................645,000 tonnes/yr.

- GRAND TOTAL (all inputs)...................................................................................................1,245,000 tonnes/yr.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 61

270 Table 28 and Figure 46 give an overview

of the estimated quantities and relative proportions

of the various oil inputs, keeping in mind the absence

of confidence limits or ranges around most of the

estimates, and the unpredictable annual occurrence

of large shipping accidents. The greatest shipping

inputs each year are from ships operational discharges (276,000 tonnes/yr.), including VOC emissions; shipping accidents (163,000 tonnes/yr.); and

coastal facilities (115,000 tonnes/yr.). Small craft

activity contributes a minimum of 53,000 tonnes/yr.

Natural oil seeps also represent a very large input, at

600,000 tonnes/yr., and essentially the same tonnage input as the total of the shipping and small craft

inputs combined (607,000 tonnes/yr.).

Figure 46.

Average annual inputs of oil into the sea from ships

and other sea-based activities

(a) by source, shown as proportions

(b) by source, shown in metric tonnes per year

(c) by source, as shown as proportions, and

including small craft activity 

271 Operational discharges from ships make

up 45% of the input of 457,000 tonnes/yr. (ships),

followed by shipping accidents at 36% of the input.

Fuel oil sludge from vessels is the major routine

operational input (186,120 or ~186,000 tonnes/yr.),

or 68% of ship operational inputs. There are important ecological reasons to try to reduce this input,

especially in coastal waters and in particularly sensitive marine areas of international importance for the

conservation of wildlife. Oil tankers, which are often

pointed at as major routine polluters, account for

10.3% of ship operational inputs, as tank washings

and oil in ballast waters. Ship accidents are a major

input still, even with the decline of large spills from

tankers in recent years; they are a very variable

source, and bad years can skew the statistics. Most

accidents are coastal, and many are damaging to the

ecology, regardless of spill size.

272 Coastal facilities contribute significantly

to the combined inputs of ships, offshore and

coastal facilities combined (19%), or 25.2% of ship

inputs. VOC emissions make up 14.9% of ship

inputs. Finally, offshore inputs, often considered by

the public as a major input, represent a minimum of

4.1% of the total input from both ships and the offshore exploration and production (E&P) combined, or

4.3% of ship inputs. Estimates of oil inputs from this

study can be compared with earlier estimates (Table

29).

Table 29.

Estimated inputs of petroleum hydrocarbons into

the ocean due to marine transportation activities

1981 1989 This study*

(million (million 1988-97

tonnes) tonnes) (mt/jr.)

Tanker operations 0.7 0.159 0.087

Tanker accidents 0.4 0.114 0.158

Bilge and fuel oil discharges 0.3 0.253 0.189

Dry-docking 0.03 0.004 0.003

Marine terminals (including

bunkering operations) 0.002 0.030 n.d.

Non-tanker accidents 0.02 0.007 0.005

Scrapping of ships - 0.003 0.015

TOTAL: 1.47 0.57 0.46

Sources: NRC (1985); IMO (1990); *GESAMP 2004 (No. 75)

Adapted from GESAMP (1993).

273 This study, as a whole, shows that ship

inputs of oil can be and have been reduced in recent

years, through cleaner ships, the use of SBT, the use

of reception facilities if available, and fewer accidents resulting in large spills. There has been significant progress reducing major sea-based activity

inputs since the 1970s. While ship inputs continue to

be reduced over the next few years, attention should

also focus on reducing the contributions of coastal

facilities, and small recreational crafts (small craft
62 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

activity). More effort is needed to ensure that legal

operational inputs from ships in all regions are

restricted to areas well away from aggregations of

marine wildlife and sensitive marine habitats. 

274 The marked decrease in operational discharges from ships over the last three decades and,

in particular, over the last 10 years may be attributed

to the greater ratification and subsequent implementation by shipping firms of MARPOL 73/78 requirements under Annex I. Aspects such as a decrease in

permissible discharge limits on waste oil for all vessel types and the introduction of segregated ballast

combined with the natural increase in newer tanker

types (accelerated phase-out of pre-MARPOL

tankers) will all contribute to a steady decrease in

future years. Significant attention to the tanker sector owing to increased public attention following

major spill incidents has meant that tanker monitoring by flag and port state authorities has been dramatically stepped up with consequent improvements

in discharge quantities. In addition, requirements

from responsible chartering parties means that most

tankers should now comply with all international legislation as a minimum, thereby decreasing the noncompliance input percentage. Further improvements

in fuel quality, engineering technology such as

enhanced purification systems, and waste oil filtering

equipment will see this decrease continue over the

next decade (2000-2010). Aside from technical

improvements adopted by the shipping industry,

many management systems have also contributed to

a greater awareness of environmental impacts and a

decrease in discharges from shipping. The mandatory introduction of the International Safety

Management Code for tankers in 1997 and the voluntary adoption of the ISO 14001 standard on environmental management will also be contributing factors to the decrease, and will be even more so in the

future.

275 A significant input noted in the study,

and not accounted for in the earlier MEPC Report

(MEPC 1990), was the VOC contribution to oil in the

marine environment. This previously unrecognized

yet substantial contribution to both atmospheric and

marine pollution has already been researched with

regards to its reduction. Having carried out a significant proportion of the research into this emission,

the tanker sector has already established a voluntary

procedure known as the VOCON, the use of which

can reduce emissions of VOC from the carriage of

crude oil by up to 80%. The refinement and further

adoption of this methodology should result in a further reduction in VOC emissions.

276 Significant efforts were made on the

assessment of tanker related discharges owing to

the detail and attention paid to this input category,

i.e. operational inputs from ships, in previous studies. The continued scrutiny of this input has meant

that a relatively accurate estimate of tanker discharge can be made, contrary to that of the other

shipping sectors. The use of the Fairplay Database

when acquiring fleet data for other vessel types may

have limited the range which can be used and the

potential for more or fewer numbers within each ship

type to be given, i.e. the use of an alternative merchant fleet database may produce different estimates. The recently completed Bunker Convention

highlights the growing attention to non-tank vessels

and the increasing quantity of bunker fuel now being

carried by some larger container and dry bulk ships,

at times well in excess of moderately sized tankers.

With the increasing diversity, size and speed of nontank vessels, a future assessment would benefit from

a more thorough investigation of this input category.

277 Small craft activity inputs are of considerable concern. They represent a significant input of

oil-derived hydrocarbons to coastal waters, but there

was no consensus as to how to make best estimates

of this input, and global data on numbers of small

craft were unavailable. This study finally took the

conservative approach, using the latest estimates

from the NRC (2003) report and projecting to a global figure of 53,000 tonnes that is included in the

overall summary of inputs (Table 28). The inputs

from small craft obviously represent a large input

source of hydrocarbons to the coastal marine environment, much better methods for and estimates of

global inputs are needed, and more regulation of

inputs is required.

278 It proved impossible to make estimates

of oil inputs from reception facilities. Reception

facilities are considered by experienced mariners to

be important oil input sources to coastal waters, but

the input data are simply not available; it is known

however that some facilities operate with good treatment, and many with little or none. It should be

noted that ships are regulated for discharges of 15

ppm, whereas the comparable restriction (guidelines

or regulations) for reception facilities is 30 ppm. 

279 Sunken ships or casualties, particularly

from past wars, represent a major threat to coastal

environments, but annual inputs of oil are currently

unknown. This problem is well recognized for island

states in the southwest Pacific. It is important for

governments to investigate sunken vessels containing oil within their EEZs, using risk assessment

methodologies that take into account factors influencing hull corrosion (Hara, pers. comm.). The threat

is serious enough to warrant concerted international

assistance and action as soon as possible.

280 The input category “Unknown sources”

proved to contribute small inputs. Oil seeps estimates were revised from the 1990 (MEPC) and earlier reports, following from NRC (2003).

281 A variety of other topics were assessed

in Section 5, for completeness. Tar (i.e. tar balls and

tar-sand lumps) is still found in many littoral (intertidal) and supra-littoral (above the tide mark) zones

worldwide. Measuring the presence, quantities and

composition of such tar in a number of carefully

selected coastal and oceanic locations, involving

local volunteers for the collections, may be one way
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 63

of monitoring ship’s operational inputs and the effectiveness of both regulations under MARPOL 73/78,

Annex 1, and relevant regulations of maritime States. 

6.2 Data and information needs

282 From this study, it is clear that data on oil

inputs from most shipping and other accidents can

be obtained through existing mechanisms. In contrast, although reliable oil input data are available

from oil production activities from the North Sea,

North America, data are not readily available from

key areas such as South America, the Gulf and

South-East Asia. Hence, input estimates from this

sector are in error by an unknown amount. 

283 Similarly, reliable data are available on

tanker operations from engineering-based calculations but data are lacking from operations and from

shipping other than tankers. Other missing data that

appear to be of major concern are the quantities of

VOC releases during loading and unloading operations of tankers. It is known that there is a substantial release of VOCs during loading, but releases during transit and unloading are less well known and

should be assessed. Quantities of VOCs entering

the ocean along shipping lanes need to be verified.

284 There is also a need for global data on oil

inputs from small pleasure craft (outboard and

inboard engines). Given the growing numbers of

small craft and their activities in more sensitive

coastal waters, efforts should be made to obtain reliable data for these activities.

285 It is vitally important to have accurate

estimates and measures of oil inputs into the sea,

both to test the efficacy of regulations and the

change of shipping and treatment practices on

behalf of cleaner marine environments, and to facilitate ecological risk assessments of oil and its components in marine ecosystems, from polar to tropical

regions. A permanent, international information

facility is needed that can collate the available data

and information on oil inputs and issue periodic

reports. 
64 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

286 The collection, analysis and interpretation of oil input data should be coordinated, taking

advantage of existing institutional data bases of

agencies and industry. How this is to be achieved

should be considered by IMO, UNESCO-IOC, ITOPF

and other relevant organizations as soon as possible.

It is particularly important to have a mechanism for

rapidly updating oil input statistics of all kinds, in

relation to ships and sea-based activities.

287 IMO could be considered as the lead

agency in this effort and take steps to co-ordinate

relevant United Nations and other organizations to

achieve the establishment of an ‘Oil and the Marine

Environment’ facility. Such a facility would collect

and collate long-term data sets, establish a database, integrate the database to a Geographical

Information System, prepare periodical reports, and

interrelate to other relevant international programmes of a similar nature, such as the Norwegian

MarMil programme. 

288 Evaluations of oil inputs from sea-based

sources, as reported above, should be carried out on

a regular basis of five years, and should cover

decades (appropriate blocks) of time since the

1990s. However, prior to conducting further input

analyses, a re-evaluation of methodologies, sources

of data and information, and necessary expertise

should be conducted, and considered to be separate

from the complex and time-consuming task of compiling the various input statistics.

289 The maintenance and precision of oil

separators on ships should be evaluated and

enhanced, in order to control and reduce operational

discharges of waste oils.

290 The databases on spills from nontankers should be strengthened.

291 Data were unavailable in the study for

discharges from reception facilities, and should be

addressed. The data from reception facilities, which

are considered crucial to solving the persistent seabased oiling problem, should include location, level

of treatment, volumes of oily water treated, and levels of total oil in discharges to coastal waters.

292 Oil inputs from small craft activity (i.e.

recreational craft) should be extensively monitored

and annually summarized. Organization and funding

of such an effort needs to be discussed within IMO.

293 Oil inputs from sunken vessels (e.g. warrelated casualties) should be selectively monitored,

given the number and location of vessels near vulnerable coastlines, and the ageing condition of the

wrecks. The risks that such inputs pose to marine

coastlines, living resources and ecosystems should

be addressed with considerable urgency, given the

aging condition of many WWII wrecks, and actions

taken to reduce those risks.

294 An international coastal tar-monitoring

programme should be initiated, to provide an up-todate global picture of chronic oiling of coastal waters

and coastlines from sea-based activities, i.e. shipping and natural sources (oil seeps). This would provide a measure of the long-term effectiveness of

both international and national pollution regulations

and guidelines followed by the shipping and oil

industries. Tar monitoring could be accompanied

with shoreline seabird monitoring, as in the Canadian

BOAS (birds oiled at sea) programme.

7 RECOMMENDATIONS
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 65

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References used while compiling the

glossary:

DST – Dictionary of Shipping Terms, 3rd Edition,

Lloyd’s of London Press.

Gold et al. (2003) Essentials of Canadian Law.

Maritime Law. 

IMO (2002). MARPOL 73/78 Consolidated

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76 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

Accident - an event that is due to human or system

error. It does not necessarily imply that there is no

fault or possible intent (pgw). Something which happens unexpectedly and unintentionally, especially

causing damage or injury. [Cambridge Internt’l.

Dictionary of English].

Accidental discharge - an unintentional release of a

substance or substances into the environment (pgw).

Accidental spillage - a release of substances or

materials into a receiving environment that is due to

human or system error. In the context of oil, it is a

release, whether intentional or not, from a point

source in one incident over a limited period of time

other than what could be normally be expected as

operational or MARPOL-permitted discharges. (See

also of the objects involved is stationary e.g. a ship

hitting a rock above water, a ship hitting a pier, a

docked ship being hit by a moving ship. [pgw]

Allision - contact with fixed or floating objects other

than ships, including docks, harbour facilities,

bridges, or offshore structures (Gold et al. 2003).

ATSDR - Agency for Toxic Substances and Disease

Registry (United States).

Ballast - heavy substances loaded by a vessel to

improve stability. Seawater is commonly loaded in

most vessels in the ballast tanks. [Sullivan 1996].

Ballast is loaded on board to obtain seaworthiness

and achieve the sea keeping abilities of the vessel

(T.J.Gunner).

Ballast oil - oil on a ship that has contaminated the

ballast water, and may be discharged with it. [pgw]

Ballast tanks - compartments at the bottom of a

ship or, in unusual cases (on bulk ore/oil carriers for

example) on the sides that are filled with liquids for

stability and to make the ship seaworthy. [Sullivan

1996].

Barge - a non-propelled, towed vessel that carries a

liquid or solid cargo, in this context oil. [pgw]. A long

boat with a flat bottom, used for carrying heavy

loads (Cambridge Dictionaries Online).

BBSR - Bermuda Biological Station for Research,

Inc.

BHP - Brake horsepower - the power of an engine

calculated in terms of the force needed to brake it.

(Concise Oxford)

Bilge - the part of the ship’s hull where the side

curves around towards the bottom [Sullivan 1996].

Lower parts of holds, tanks and machinery spaces

[Swindells 1997]. Area of a lower part of a hold

where liquids collect and are pumped out at regular

intervals [Brodie 1996]. 

Bilge oil - oil from the area in the lower part of the

hold where surplus liquids collect and are pumped

out at regular intervals. [fm/dst]

Bilge tanks - tank(s) on a vessel in which bilge water

is stored [pgw].

Bilge water - accumulated water in bilges that has

no use [Sullivan 1996]. A mixture including water

and oil collected in the bilge of the machinery space

in a ship as a result of leakage, drainage, etc. [IMO

1998]. The dirty water that collects in the bottom

inside part of a ship. [Cambridge Dictionaries

Online].

Blowout - an unintended and uncontrolled release of

oil and/or gas at a wellhead, often under great pressure. Can occur on a platform or on the sea floor.

BOAS - birds oiled at sea program. An Environment

Canada (Canadian Wildlife Service) programme monitoring the presence of oiled seabirds in offshore

Atlantic Canada and along coastal Newfoundland,

and relating such oiling to discharges (legal and illegal) from ships.

Bunker - a tank or compartment (on a boat or ship)

for the storage of fuel. [Sullivan 1996].

Bunker oil - any hydrocarbon mineral oil, including

lubricating oil, used or intended to be used for the

operation or propulsion of the ship, and any residues

of such oil. (Source: Draft International Convention

on Civil Liability for Bunker Oil Pollution Damage,

IMO, 2000)

Bunkering - replenishing the ship with fuel. [Sullivan

1996]

Cargo tanks - ship’s tanks used for the carriage of

cargo as opposed to, for instance, a ballast tank.

[Brodie 1996].

Casualty - a serious or fatal accident. A person or

thing injured, lost or destroyed. A disastrous occurrence due to sudden, unexpected or unusual cause.

Accident; misfortune or mishap; that which comes

ANNEX

GLOSSARY AND ACRONYMS*

* Please note: The source reference for each term is identified, in brackets, after the definition or description. MARPOL

Annex I definitions (IMO 2002, p. 45-49) take precedence

wherever relevant to this topic. The purpose of this glossary

is to explain terms that are prominent in the text and important to clarify for the reader.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 77

by chance or without design. A loss from such an

event or cause; as by fire, shipwreck, lightning, etc.

[Black 1979].

CBT - clean ballast tanks - tanks on tankers used

solely for ballast [pgw]

Clingage factor - an estimation of the percent of oil

retained in a tank (fuel or cargo) due to its adherence

to the tank walls and other surfaces (pgw).

Coastal Zone - a zone comprising coastal waters

(including the lands there under) and the adjacent

shore-lands; the zone strongly influenced by both

sea and land and including smaller near-coast

islands, transitional and inter-tidal areas, wetlands

(mangroves and marshes) and beaches. [Clark 1998]

Coastal facility - in context of this report, it is any

industrial infrastructure associated with the processing and transport of oil carried by ships, or coming

ashore from the offshore production activities [pgw]

CONCAWE - Oil Companies’ European Organization

for Environment and Health Protection.

COW - crude oil washing, or crude oil washing system, is a cargo tank cleaning system that uses crude

oil as the washing medium (see section 3.2) (tw,

IAITO)

CPP - clean petroleum product. Refined products

such as aviation spirit, motor spirit and kerosene.

Also referred to as clean products or white products.

[Brodie 1996].

CRUCOGSA - a Norwegian research programme

studying the physical behaviour of crude oil influencing its carriage at sea.

DH - double hulled.

Discharge - release of a substance or material into a

receiving environment. Discharges may be legal or

illegal, intentional or unintentional. [pgw]. In relation

to harmful substances or effluents containing such

substances, means any release howsoever caused

from a ship and includes any escape, disposal,

spilling, leaking, pumping, emitting or emptying.

[IMO 1997a].

DNVPS - DNV Petroleum Services. An international

company based in London, United Kingdom, and

Houston, Texas.

Double-hulled (DH) tanker - a tanker with both

inner and outer bottom plating on the hull. [adapted

from Swindells 1997]. System in tankers whereby an

inner hull serves as protection against oil spills in the

event of a ship running aground or coming into contact with another ship or solid object. Sometimes

referred to as a double skin. 

DPP - dirty petroleum product. Crude oils and their

products, such as heavy fuel oils. Also referred to as

black products. [adapted from Brodie 1996].

Drill cuttings - the solids resulting from drilling into

sub-surface formations, and which are brought to

the surface of the well in the drilling-fluid system.

[GESAMP 1993].

Dry docking - the process by which a boat or ship

enters a shipyard, for repairs and/or maintenance,

and is taken out of the water.[pgw]

Dry bulk - cargo shipped in a dry state and in bulk,

for example, grains, ore or cement. [Sullivan 1996].

Drybulker - a ship carrying a bulk cargo of a dry

and/or solid (non-liquid) nature [pgw]

Deadweight - difference between a ship’s loaded

and light displacements, expressed in tons or

tonnes. [Brodie 1996].

DNVPS - DNV Petroleum Services.

DPP - dirty petroleum product (usually in reference

to a vessel carrying such products).

DWT - dead-weight tonnage or DWT is the number

of English long tons (each weighing 2,240 lb.) that a

vessel is capable of transporting, including cargo,

passengers, crew, stores, and bunker fuel (Gold et al.

2003).

E&P Forum - Exploration and Production Forum.

(based in London, United Kingdom).

EDF - Environmental Defense Fund (USA).

ESP - Enhanced Survey Program, for ships in dry

docks

Effluent - a liquid discharge, untreated or treated,

from a fixed (point-source) industrial or municipal

site. [pgw]. (civil engineering) 1. Liquid waste water

that results from sewage treatment or industrial processing. 2. Such waste liquid released into waterways. (chemical engineering). Any liquid or gas that

is discharged from a processing operation. [Morris

1992].

ERC - Environmental Research Consulting (USA).

Estimation - the process of developing estimates,

which are defined as the most reasonable, quantitatively-derived numbers describing a process, behaviour or event [pgw]

Estuary - a semi-enclosed littoral basin (embayment)

of the coast in which fresh river water entering at its

head mixes with saline water entering from the

ocean. [Clark 1998]. Places where seawater is

measurably diluted with fresh water; estuaries may

take the form of well-demarcated valleys, semienclosed bays, or shallow lagoons often associated

with sandbars at their seaward edge. [Mann 2000]. 

Flaring - the process of burning off waste or unwanted gases; commonly used on offshore oil and gas
78 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

production platforms. [adapted from Swindells

1997]

FOBAS - 

FPSO - floating production, storage and offloading

unit. Used in the offshore oil and gas industry. [jc]

FSO - floating storage and offloading unit. [fm/dst]

Fuel oil - the heaviest grades of residual fuel used

for marine and industrial purposes. [Sullivan 1996].

See Table 2 in ISO 8217:1996.

Fuel oil sludge - residual oils and other substances

that collect at the bottom of a ship’s bunker tanks.

[pgw]

Gallon - an Imperial gallon is 4.54 litres; a US gallon

is 0.833 of an Imperial gallon or 3.782 litres (see units

and conversion table) 

Gas-freeing - the process of cleaning dangerous

and explosive airs or gases from empty petroleum

tanks. [Sullivan 1996].

GESAMP - the Joint Group of Experts on the

Scientific Aspects of Marine Environmental

Protection (formerly Marine Pollution), established in

1969. It is an advisory group to the United Nations

and its bodies. It consists of both natural and social

scientists, and encourages collaboration and coordination of activities within the United Nations system

on matters relating to marine pollution and marine

environmental protection. (Wells et al. 2002).

GIS - geographic information system(s). Computerassisted systems that can input, store, retrieve,

analyse and display geographically referenced information and enhance the analysis and display of

interpreted geographic data (Clark 1998).

GPA - Global Programme of Action for the Protection

of the Marine Environment from Land-based

Activities. Otherwise known as the Washington

Protocol, signed November 1995.

HBL - Hydrostatic balance loading (of tankers).

Hydrocarbons - A combination of hydrogen and carbon often found in gas and oil. [Sullivan 1996].

IGO - inter-governmental organization.

Illegal operational discharge - under MARPOL for

oil, that would be a discharge of >15ppm or >30

litres oily waste per nautical mile within 50 nautical

miles from a coastline. [pgw]

Illegal spill - the release of a material or substance

into a receiving environment e.g. coastal or marine

waters, that is not sanctioned by law, either national

or international. [pgw]

ILO - International Labour Organization (United

Nations).

IMO - International Maritime Organization (United

Nations).

Incident - “means an event involving the actual or

probable discharge into the sea of a harmful substance, or effluents containing such a substance”

(IMO 1997, MARPOL 1973/78 volume)

Incidental discharge - same as an incident.

Intentional discharge - a release of oil done on purpose, not by accident. (pgw). Mitchell (1994) “uses

the terms intentional discharges and operational discharges interchangeably, the point being to distinguish them from accidental oil spills. (p. 71)

INTERTANKO - International Association of

Independent Tanker Owners, located in London,

United Kingdom.

IOSD - International Oil Spill Database - a database

of individual records of oil spill incidents maintained

since 1978 by Cutter Information, Cambridge, MA.,

USA.

ISO - International Standards Organization.

ITOPF - International Tanker Owners Pollution

Federation Limited.

Legal discharge - a discharge of oil condoned by

law, either national or international. (pgw). Mitchell

(1994) states that “tankers have essentially three

legal methods of disposal available: discharge slops

at sea within prescribed limits on content and rate

and constrained by the total discharge standards,

discharge slops during delivery by using LOT, and

discharge slops at reception facilities after the ballast voyage” (p. 80-81).

Littoral (zone) - the intertidal zone, or the area of a

beach between high water and low water marks

[pgw]. The shoreline where a normal cycle of exposure and submersion by the tides occurs. [Morris

1992].

LOT - the load-on-top principle (see the MARPOL

Convention Annex 1). The practice of loading a fresh

cargo of oil on top of oil recovered from tank cleaning operations. Widely used on tankers engaged in

the crude oil trade. The onboard water and oil mixture from ballasting and cleaning of tanks is pumped

ashore at loading terminals with special reception

facilities to reduce the risk of oil pollution at sea.

[Swindells 1997]. 

MARPOL 73/78 - the International Convention for the

Prevention of Pollution from Ships, or Articles,

Protocols, Annexes, Unified Interpretations of the

International Convention for the Prevention of

Pollution from Ships, 1973, as modified by the

Protocol of 1978 relating thereto (IMO 1997a, 2002).

It is the primary international convention dealing with

pollution from ships and shipping, covering oil, chemical substances, sewage, garbage and air pollution.
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 79

Machinery - the main engine(s) and auxiliaries in a

ship including deck machinery such as capstons,

winches, pumps, lifts and door and ramp operating

system. [Sullivan 1996].

Machinery space bilges - the lower parts of the

machinery space of a ship [adapted from Swindells

1997]

Machinery space oils - oils from engines and other

machinery on a vessel that end up in the bilge (also

see definition of bilge water).

MDO - marine diesel oil.

MEPC - Marine Environment Protection Committee

(of IMO).

Metric tonne - equivalent to 2,205 lb, in contrast to

an Imperial or British ton of 2000 lb.

MMS - Minerals Management Service (United States).

MTBE - a chemical additive in gasoline, namely

methyl tert-butyl ether (Gabele and Pyle 2000). 

NA - North America(n)

Non-tankers - ships that are not carrying a liquid

cargo [pgw]

Non-oil cargo vessels - ships carrying cargo other

than oil [pgw]

ODME - oil discharge monitor.

OGP - The International Association of Oil and Gas

Producers (based in London and Brussels).

OILPOL 1954 - International Convention for the

Prevention of Pollution of the Sea by Oil 1954,

amended in 1962 and 1969. Now effectively superseded by MARPOL 73/78. [Sullivan 1996]

Oil – for the purpose of Annex 1 of MARPOL 73/78,

means petroleum in any form including crude oil, fuel

oil, sludge, oil refuse and refined products (other

than petrochemicals) [IMO 1997a].

Oil-based muds (OBM) - drilling fluids used at the

well that contain hydrocarbon-based lubricants.

[from GESAMP 1993]

Oil discharge - release of oil or oil-containing substance(s) into the marine environment [pgw].

Oil fingerprinting - analytical chemistry techniques

used, often in combination, for identifying the source

(s) of an oil. [pgw]. Recent fingerprinting systems

use the unique characteristics of oil from different oil

fields to distinguish the responsible tanker (source of

a spill) from several suspects [adapted from Mitchell

1994]. Advanced techniques are described in Bence

and Burns (1995), Boehm et al. (1997), and Page et

al. (1995, 1998).

Oil sheen - an extremely thin layer or film of petroleum product causing some visual evidence on the

water surface. [IMO 1998].

Oil slick - film of oil on the surface of the water

[Sullivan 1996]. Usually caused by accident or

spillage but can also be caused by natural oil seepage from the ocean floor. [Swindells 1997]. A thin

film of oil on water. [IMO 1998b]. The oil in a slick can

be mineral, vegetable or fish oil in origin.

Oil tanker - ship designed specifically for the carriage of oil in bulk. They range from a small coastal

tanker usually carrying a finished product to an ultra

large crude carrier (ULCC) that may be half of a million tons deadweight. [Swindells 1997].

Operational discharge - a release of a material or

chemical from a ship, whether legal or illegal. Legal

operational discharges of oil from ships are regulated under the MARPOL Convention (Annex 1).

Operational losses - intentional or unintentional

losses of oil and oily wastes to the sea from the routine operation of a ship or offshore oil platform

[pgw] 

PAHs - polycyclic aromatic hydrocarbons - components of oil consisting of two or more fused aromatic (benzene) rings e.g. naphthalenes, phenanthrene,

benzo-a-pyrene. [adapted from Neff 1979].

PCBs - polychlorinated biphenyls.

Pelagic - an oceanographic term meaning open

ocean or water column.[pgw].

PSC - Port State Control.

Produced water - generated from oil and gas production operations. It consists of formation water

(the water naturally present in the reservoir), flood

water previously injected into the formation to maintain pressure, and/or, in the case of some gas production, condensed water. Its composition is quite

complex and highly variable, consisting of water, dissolved and dispersed oils, salt and many other inorganic and organic constituents. [Adapted from

Exploration and Production Forum 1994].

Reception facility - for oily residues and oily wastes,

they are fixed installations and mobile or floating

processing plants that exist at ports around the

world to receive and treat oily waste and residues or

slops from ships. [adapted from Sullivan 1996]

Recreational boating - boating, in small powered,

partially powered or un-powered vessels, conducted

for non-work purposes. [pgw].

Recycling - with reference to ships, see Scrapping.

Reefer vessel - ship having refrigerated holds for

the transport of cold fruit and/or vegetables, or

frozen cargo.
80 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

SBT - segregated ballast tank - a ballast only tank

into which seawater used as ballast is loaded, and

discharged through a separate piping and pumping

system. [adapted from Swindells 1997].

SBT/DH - segregated ballast tank/double hulled (in

reference to an oil tanker).

Scrapping - the process by which a ship is beached

and broken up/ dismantled for scrap metal and other

materials. [pgw]. “Ships are not scrapped but recycled, conforming with one of the basic principles of

sustainable development. Recycling is defined by

the World Wildlife Fund as ‘the processing of waste

or rubbish back into raw materials so that it can be

made into new items’. It is undoubtedly beneficial –

to the individual, the community and the planet”

(Source: Report of ship recycling correspondence

group to MEPC 46, IMO).

Sea-based activity (ies) - in context of this report

and its mandate, it “includes all forms of shipping,

especially in oil tankers and carriers, other commercial and non-commercial ships, as well as transportation through marine pipelines. They would further include offshore and coastal exploration and

production, atmospheric emissions from such seabased activities, coastal refineries and storage facilities, oil contaminated material disposed of at sea,

and natural marine oil seeps”.

Seeps - also called natural oil seeps. There are

areas of the earth’s crust where crude oil from underground reservoirs moves by natural forces to the surface. Located on land or underwater. [pgw]. A naturally occurring emergence of liquid petroleum at the

(earth’s) surface as a result of a slow, upward migration from its source through minute pores or fissures.

(Academic Press, Dictionary of Science and

Technology).

Ship - “means a vessel of any type whatsoever operating in the marine environment and includes hydrofoil boats, air-cushion vehicles, submersibles, floating craft and fixed or floating platforms”. (IMO

1997a).

Slops - tank cleaning residues retained on board a

tanker in the slop tank for eventual disposal ashore

or mixture with incoming cargo. [Sullivan 1996].

Mixture of water and oil residues from cargo tanks in

oil tankers that may contain oil/water emulsions,

paraffin wax, sediments and other tank residues.

[IMO 1998]. Residue of a ship’s cargo of oil together with the water used to clean the cargo tanks.

[fm/dst].

Slop tank - tank in a tanker into which slops are

pumped. [fm/dse]

Sludge - Deposits, generally from the purification of

fuel and lubrication oils, consisting of mixtures

including oil, paraffin wax, sediments and other tank

residues. [IMO 1998b]. Oil sludge is heavy oily

material that collects at the bottom of oil tanks (fuel

or cargo) on a ship [pgw]. 

Sludge oil - as defined in MARPOL, is sludge from

the fuel or lubricating oil separators, waste lubrication oil from main or auxiliary machinery, or waste oil

from bilge water separators, oil filtering equipment or

drip trays (IMO 2002).

Small craft - boats, predominantly leisure craft,

operating on either 2 or 4-stroke engines. They are

25 m or under in length at the waterline.[pgw]

SOLAS - Convention on Safety of Life at Sea (IMO).

Sovereign immunity - Doctrine precludes litigant

from asserting an otherwise meritorious cause of

action against a sovereign or a party with sovereign

attributes unless sovereign consents to suit. [Black

1979].

Spill - release of a substance or material from a

source into a receiving environment. Spills may be

legal or illegal, intentional or unintentional. [pgw]

Spills (small) - within the context of this GESAMP

report, they are spills of oil between 0.17- 34 tonnes

(50 US gal - 10,000 US gal.). [dse]

Spill estimation factor - a statistically derived value

that is applied to the IOSD oil spill database in order

to derive estimates of numbers and volumes of

smaller spills (dse).

Spillage - the quantity of oil spilled from a particular

incident (as opposed to the number of spills). (fm)

Standard - A legally enforceable numerical limit or

narrative statement, such as in a regulation, statute,

contract, or other legally binding document, that has

been adopted from a criterion or an objective.

[CCME 1999]. A level of quality. [Cambridge

Dictionaries Online]. 

Tank washings - tank washing water containing

cargo tank residues including oil, paraffin wax, sediment and other foreign matter such as tank cleaning

chemicals. [IMO 1998].

Tanker - a ship constructed to carry liquid cargoes in

bulk, in this context oil. They come in various sizes.

[adapted from Sullivan 1996]. From ITOPF (2005),

“tanker” means any ship (whether or not self-propelled) designed, constructed or adapted for the carriage by water in bulk of crude petroleum, hydrocarbon products and other liquid substance.

Tar balls - lumps of oil that form from oil discharged

from ships, largely from the ballast of crude oil

tankers, and that float on or near the sea surface,

weather (i.e. lose fractions of the oil, becoming hardened and encrusted with organisms externally), and

often contaminate coastlines and amenity beaches.

[pgw]. Compact semi-solid or solid masses of highly

weathered oil formed through the aggregation of viscous, high carbon number hydrocarbons with debris

present in the water column; tar balls generally sink

to the sea bottom but may be deposited on shore-
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 81

lines where they tend to resist further weathering.

(Doerffer 1992). Oil that has evaporated and possible

mixed with debris and has formed into a solid mass

or solid form. [IMO 1998b].

Ton - an Imperial or British unit of weight equivalent

to 2000 lb. [GESAMP 1993]; the weight ton is usually expressed in terms of the American short ton

(2000 lb. or 907 kg.) (Gold et al. 2003). The English

long ton is 2,240 lb or 1016 kg (Gold et al. 2003).

Tonne - a metric tonne, equivalent to 1000 kg or

2,205 lb. [GESAMP 1993; Gold et al 2003]

UNCED - United Nations Conference on

Environment and Development. This conference was

held in Rio de Janeiro in 1992 and produced Agenda

21 as well as several treaties.

UNCLOS - United Nations Convention on the Law of

the Sea. It was signed in 1982 and formally became

international law in 1994.

UNEP - United Nations Environment Programme.

The environmental programme of the United Nations

based in Geneva, Manila, Nairobi and The Hague

(see www.unep.org). 

Uncertainty factor - definition needed (p. 40, draft 3)

Venting - in the offshore sector, this refers to the

release of gas at a well site [pgw]

VLCC - very large crude carrier.

VOCs - volatile organic compounds. Defined in

the Clean Water Act (USA) to include all

volatile hydrocarbons except methane, ethane, a

wide range of CFCs or chlorofluorocarbons, HCFC

(hydrochlorofluorocarbons), and a few others

e.g. acetone (NRC 2003, p. 71) In the context of

activities of the offshore oil industry, VOCs are categorized as methane and non-methane hydrocarbons.

[pgw] VOCs are considered under Regulation 15,

Annex VI, MARPOL, in the context of vapour emission control on tankers, and non-methane VOCs on

gas carriers.

VOCON - a procedure developed by Intertanko

which utilizes onboard equipment to help the crew of

a ship minimize unnecessary cargo boil-off (The

MotorShip, the Marine Technology Magazine, May

26th, 2004).

Volumes (gross, loaded, shore-based) - gross volume is the total volume, including entrained water,

delivered as cargo to a tanker, and corrected to a

temperature of either 15 degrees C or 60 degrees F.

A loaded volume is the same as gross volume. A

shore- based volume is the same as gross volume by

convention. (T.J.Gunner)

WWI and WWII - World War One, 1914-1918; World

War Two, 1939-1945.
82 · ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES GESAMP Report and Studies No 75

1 Framework for evaluating sources of inputs of

oil in the sea from sea-based activities

2 Cumulative percentage of total oil spillage

(numbers of spills and amounts) by size class,

US vessel spills (1985-1999)

3 Cumulative percentage total oil spillage from

facilities and pipelines into US marine waters

(numbers and amounts spilled) by spill size

class (1985-1999)

4 Accidental oil spills from all source types into

the marine environment (1988-1997)

5 Percent of vessel spill numbers involving at

least 5,000 tonnes of oil

6 Regional oil spill analysis, showing the 18 geographic regions

7 Total non-military-related oil spills from all

sources (spills of at least 34 tonnes)

8 Total oil spillage from all sources (spills of 34

tonnes and over)

9 Estimated annual oil spill input for ten-year

periods by source type, excluding military incidents

10 Total oil input into marine environment by

source type 1968-1977

11 Total oil input into marine environment by

source type 1978-1988

12 Total oil input into marine environment by

source type 1988-1997

13 Average annual oil spill input by source type

1988-1997

14 Estimated annual oil spills from tankers 1968-

1999 – amounts spilled and estimated number

of spills

15 Estimated annual oil spills from tankers 1968-

1999 – amounts spilled with >50,000 tonne

tanker spills identified

16 Estimated annual oil spills from non-tankers

1968-1999 – amounts spilled and number of

spills

17 Oil movement by tankers worldwide (millions of

tonnes)

18 Major oil trade movements 1997

19 Estimated oil spillage in Region 1 (Northeast

Pacific Ocean)

20 Estimated oil spillage in Region 2 (Southeast

Pacific Ocean)

21 Estimated oil spillage in Region 3 (North

Atlantic Ocean)

22 Estimated oil spillage in Region 4 (Gulf of

Mexico/Caribbean Sea)

23 Estimated oil spillage in Region 5 (Southwest

Atlantic Ocean)

24 Estimated oil spillage in Region 6 (Northeast

Atlantic Ocean)

25 Estimated oil spillage in Region 7 (North Sea)

26 Estimated oil spillage in Region 8 (Baltic Sea)

27 Estimated oil spillage in Region 9

(Mediterranean Sea)

28 Estimated oil spillage in Region 10 (Black Sea)

29 Estimated oil spillage in Region 11

(West/Central African Atlantic)

30 Estimated oil spillage in Region 12 (Southern

Africa)

31 Estimated oil spillage in Region 13 (Eastern

African Indian Ocean)

32 Estimated oil spillage in Region 14 (Red

Sea/Gulf of Aden)

33 Estimated oil spillage in Region 15 (Gulf Area)

34 Estimated oil spillage in Region 16 (Arabian

Sea/Indian Ocean)

35 Estimated oil spillage in Region 17 (East

Asian/Southeast Asian Seas)

36 Estimated oil spillage in Region 18

(Australian/New Zealand Pacific)

37 Regional oil spill analysis (oil spills over 5,000

tonnes 1988-1997)

38 Worldwide distribution of offshore oil and gas

platforms

39 Inputs of oil on cuttings into the North Sea

40 Produced water discharge to the North Sea

41 Input of oil from produced water discharges to

the North Sea

List of Figures
GESAMP Report and Studies No 75 ESTIMATES OF OIL ENTERING THE MARINE ENVIRONMENT FROM SEA-BASED ACTIVITIES · 83

1 Regional descriptions for regional data anlysis 

2 Ship types, numbers and average brake horsepower (BHP)

3 Estimation of total bunker consumption per

vessel

4 Discharge of fuel oil sludge from vessels in

tonnes, on assumption of 100% compliance

with MARPOL Annex 1

5 Operational oil outflow estimates in tonnes,

based on 86% compliance with MARPOL legal

limits

6 Tanker types and tonnage distribution (circa

2000)

7 Tonnage distributions, in tons dwt, of chemical/oil tankers for long- and short-haul voyages, after correction for proportions used in

Annex I cargoes

8 Tonnage distributions, in tons dwt, of product

tankers for long- and short-haul voyages

9 Tonnage distributions, in tons dwt, of crude

tankers for long- and short-haul voyages

10 Matrix of voyage frequency (laden voyages per

annum) for vessel type and size

11 Total tonnage of oil (Annex 1 cargoes) shipped

by the world’s tanker fleet (100% dwt, in million tons)

12 Outflow matrix for calculations of oily waste

discharge from tanker cargo operations assuming 100% loading

13 Outflow matrix for calculations of oily waste

discharge from tanker cargo operations including part-cargo carriage estimates

14 The final outflow matrix for calculations of oily

waste discharge from tanker cargo operations,

in tonnes

15 Summary matrix of operational discharges –

cargo-related (values in tonnes/yr.)

16 Annual number of accidental, sea-based oil

spills of 34 tonnes and over (based on ERC

database)

17 Annual oil spillage, in tonnes, from spills of 34

tonnes and over (based on ERC database)

18 Estimated average annual oil input from ships

and other sea-based activities, in tonnes, for

three, ten-year time periods (based on ERC

database)

19 Estimated average annual oil input, in tonnes,

for three, ten-year time periods – a summary

(based on ERC database)

20 Estimated annual average input, in tonnes, from

smaller and large spills, by source type (based

on ERC database)

21 Worldwide Tanker Spills since 1960, Over

50,000 tonnes. Recent, well-publicized,

European spills such as Erika (1999) and

Prestige (2002) are not shown, nor is the wellknown Exxon Valdez spill which was only 37-

38,000 tonnes.

22 Inter-area oil movements 1997 (million tonnes)

23 Average annual percentage of oil spilled, per oil

tonnage transported by tankers

24 Input of oil into the North Sea of oil-based fluids on drill cuttings, in tonnes

25 Oil inputs to the North Sea from discharges of

produced water

26 Estimated maximum coastal oil refinery effluent

output, regional estimates (1988-1997)

27 Estimated maximum coastal oil refinery effluent

output, national estimates (1988-1997)

28 Estimated average annual inputs of oil, in

tonnes per year, into the sea from ships and

other sea-based activities

29 Estimated inputs of petroleum hydrocarbons

into the ocean due to marine transportation

activities

42 Estimated annual oil spills from exploration and

production facilities 1968-1999

43 Estimated annual oil spills from marine

pipelines 1968-1999

44 Estimated annual oil spills from coastal facilities 1968-1999

45 Annual amount of oil spilled from unknown

sources (1968-1997)

46 Average annual inputs of oil into the sea from

ships and other sea-based activities

List of Tables
Science for Sustainable Oceans

ISBN 978–92–801–4236–5

ISSN 1020–4873

IMO FAO UNESCO IOC WMO UNIDO IAEA UN UNEP