GEOLOGICAL SURVEY CIRCULAR 694 

The Worldwide Search 

for Petroleum OffshoreA Status Report for the 

Quarter Century, 19 47-72 

The Worldwide Search 

for Petroleum OffshoreA Status Report for the 

Quarter Century, 1947-72 

By Henry L. Berryhill, Jr. 

GEOLOGICAL SURVEY CIRCULAR 694 

1974 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, National Center, Reston, Va. 22092 
CONTENTS 

Page 

Abstract ---------------------------------------------------------------- Introduction 

1 

1 

3 

5 

5 

Scope of the search ------------------------------------------------------

Results of exploration ----------------------------------------------------

Number and geographic distribution of fields discovered ----------------

Chronology of offshore discoveries _____ ---- ______ ---- _ ----------------- 10 

16 

20 

23 

26 

Offshore petroleum reserves and production ----------------------------

Geologic summary of the world's offshore producing areas -------------------

Conclusions -------------------------------------------------------------

References cited ---------------------------------------------------------

ILLUSTRATIONS 

Page 

FIGURE 1. 

2. 

3-5. 

World map showing oceans and seas and 2,500-m isobath ---------

Diagrammatic profile of the continental margin -----------------

World maps showing: 

4 

5 

3. Generalized offshore areas under concession for exploration_ 6 

4. Disposition of offshore drilling rigs owned by United States 

companies ------------------------------------------ 7 

5. Giant oil and gas fields relative to generalized orogenic 

belts ----------------------------------------------- 9 

6. Graph showing chronology of discovery of offshore giant oil and 

gas fields -------------------------------------------------- 11 

7. Graph showing sea-state conditions in selected offshore areas and 

the effect on drilling and supply operations -------------------- 13 

8. Map and graph showing relation of offshore oil reserves and production to total world oil reserves and production ------------- 18 

9. World map showing thickness of sedimentary deposits in the submerged continental margins --------------------------------- 21 

10. World map showing distribution of known major evaporite deposits 

offshore ---------------------------------------------------- 24 

TABLES 

Page 

TABLE 1. Numbers of offshore petroleum fields listed by continent and country_ 8 

2. Discovery and development time for the giant offshore petroleum 

fields ------------------------------------------------------- 12 

3. Time span and costs for finding and developing an oil field in the 

North Sea -------------------------------------------------- 14 

4. Provisional estimated recoverable reserves and cumulative production offshore ------------------------------------------------ 16 

5. Provisional worldwide estimated recoverable offshore gas reserves 

and cumulative production ----------------------------------- 17 

6. World's largest oil fields --------------------------------------- 19 

7. Characteristics of giant offshore petroleum fields relative to geologic 

setting ----------------------------------------------------- 23 

III 

The Worldwide Search for Petroleum OffshoreA Status Report for the Quarter Century, 

1947-72 

By Henry L. Berryhill, Jr. 

ABSTRACT 

At the end of 1972, offshore petroleum exploration 

was in progress on the submerged continental margins 

of 80 countries. Some 780 oil and gas fields had been 

discovered. Estimated worldwide volume of oil discovered offshore as of January 1, 1973, is 172.8 billion 

barrels of oil, or about 26 percent of the world total, 

and 168.4 trillion ft3 of natural gas. Present reserves 

of oil are 135.5 billion barrels, of which 70 percent is 

in the Persian Gulf. Some 90 percent of the oil discovered offshore has been found in 60 giant fields having 

reserves of 500 million or more barrels each. 

INTRODUCTION 

During the past decade the search for petroleum on the submerged continental margins of 

the world has accelerated at a rate surpassing 

earlier forecasts. The floors of the world's 

oceans and seas adjacent to the continents are 

the major exploration focus of a large segment 

of the petroleum industry, and the offshore 

search in progress has been referred to as the 

beginning of one of the most massive oil-hunting eras in history (McCaslin, 1972, p. 106) 

Awareness of the presence of oil and gas in 

the rocks beneath the oceans is neither a recent insight nor the result of a single dramatic 

new development in exploration techniques. Development of the capability to find and produce 

large quantities of petroleum from beneath 

the sea floor has been a growth process that is 

but the latest chapter in the history of the 

petroleum industry. 

The first interest in the production of petroleum from the offshore came with the discoveries of sizable fields onshore immediately adjacent to the shoreline of such places as California and Lake Maracaibo. As early as 1896, 

petroleum was produced offshore from a sea1 

ward extension of the Summerland field, California (Yerkes and others, 1969). Drilling was 

done from wooden piers built outward from 

shore. In 1923, the Venezuelan Gulf Oil Company acquired concessions extending 1 km off 

the shores of Lake Maracaibo. In 1926, the 

initial discovery was made in the Lagunillas 

field in the shallow waters of Lake Maracaibo 

(Oil and Gas Journal, 1959). Lagunillas proved 

to be a giant field, and its discovery indicated 

that additional oil and gas deposits lay farther 

out in deeper water. Methods developed for 

offshore operation at Lagunillas became world 

famous and helped pave the way for future 

operations (Critz, 1947). Discovery of oil on 

Bahrain Island in 1932 brought the realization 

that substantial amounts of petroleum might lie 

beneath the waters of the Persian Gulf. The occurrence of large and productive salt domes 

along the coast of the Gulf of Mexico in Texas 

and Louisiana suggested that the oil-bearing 

province extended offshore, and in 1938 oil was 

discovered off Louisiana in 8 m of water a mile 

(1.6 km) from shore. Through 1946, nine wells 

were drilled in the Gulf of Mexico, five off 

Louisiana and four off Texas. All were in shallow water close to shore, and all were drilled 

from rigid platforms (Critz, 1947). 

The developments in offshore petroleum exploration summarized herein had their beginning in the Gulf of Mexico during the summer 

and fall of 1947. The first subsea well completed 

from a mobile platform was in the Gulf of 

Mexico, and drilling thereafter was no longer 

limited to the water-depth restrictions of the 

rigid platform that had to be built in place. 

Using two World War II surplus Navy barges 
and a surplus Navy LCT converted to form a 

drilling platform, Kerr-McGee Oil Industries, 

Inc. discovered oil in Ship Shoal Block 32 on 

October 4, 1947, 12 miles (19.2 km) from the 

Louisiana shore (Seale, 1948). The ability to 

drill successfully from a mobile platform was 

demonstrated, and the era of large-scale exploration and production from the offshore was 

launched. 

The prelude to the Kerr-McGee discovery had 

been the events and activities in the United 

States during the few years prior to 1947 that 

indicated the mounting interest of both industry and the Federal Government in the 

petroleum possibilities of the offshore. During 

the late 1930's, industry had become increasingly active in geophysical exploration in shallow 

waters close to shore. In 1943, as a result of 

war demands and petitions for leases in the tidelands of California, the Department of the Interior investigated the possibilities of exploring 

and producing petroleum from the offshore 

areas. In 1945, the Congress, seeking additional 

petroleum resources, held a series of hearings 

on possible new sources. During these investigations the Director of the U.S. Geological Survey, W. E. Wrather, pointed out that the continental shelves of the United States, as well as 

those around the world, are potential oil-bearing areas (U.S. Senate, 1945). The Senate investigations resulted in an action that was to 

have a significant impact on future development of petroleum resources offshore. On September 28, 1945, President Truman issued a 

proclamation asserting "that the exercise of 

jurisdiction over the natural resources of the 

sub-soil and seabed on the continental shelf by 

the contiguous nation is reasonable and just 

.... the continental shelf may be regarded as 

an extension of the land mass of the coastal nation and thus naturally appurtenant to it." In 

November 1946, Everett DeGolyer, in a speech 

before a meeting of the Independent Natural 

Gas Association, announced that geophysical 

studies in the Gulf of Mexico within the 10-m 

water depth between the Sabine River and the 

Mississippi River indicated at least 30 salt-dome 

structures of both piercement and nonpiercement types that were similar to those already 

producing petroleum along the Gulf coast 

(Critz, 1947). Thus the pattern was established 

2 

that would guide offshore exploration in the 

years ahead : ( 1) Explore first those areas immediately adjacent to established onshore production, (2) search for similar easily discovered structures, and (3) explore for the harderto-find structures. By the end of 1946, Louisiana, then claiming seaward proprietorship 

of the sea floor to 27 miles ( 43 km) from shore, 

had leased 675,385 acres on the offshore and 

a number of companies were actively exploring (Critz, 1947). 

In the few years after 1947 came the controversy between the maritime States and the 

Federal Government over jurisdiction of the 

seabed of the continental shelf. The legal disputes and court proceedings involved in the 

controversy delayed development of offshore 

petroleum resources for some 6 years. On 

August 7, 1953, President Eisenhower signed 

the Outer Continental Shelf Lands Act, which 

provided the immediate leasing of Federal offshore areas by the Department of the Interior 

and the validation of leases previously issued 

by the states. In decisions in 1954, the Supreme 

Court settled the jurisdictional boundary disputes by giving proprietorship of the inner 3 

miles ( 5.8 km) of the shelf to the maritime 

states. In separate decisions, Texas was given 

jurisdiction 3 leagues seaward (10.3 miles, 

16.5 km) and Florida was likewise granted a 

3-league jurisdiction over that part of its offshore in the Gulf of Mexico. Federal jurisdiction was established for that part of the shelf 

seaward from the State boundaries, and the 

first Federal lease sale was held in 1954. 

The petroleum industry moved to the offshore 

in response to increasing consumer demands 

which no longer could be met adequately by 

onshore sources. The year 1947 is significant 

not only as the beginning of the "modern era" 

of offshore exploration but also as the last year 

in which the United States was a net exporter 

of petroleum. The year 1948 was the first full 

year in which the United States reversed its 

historical position as a net exporter and became a net importer of oil (World Oil, 1948). 

The trend has not been reversed, and the United 

States now imports nearly 40 percent of its 

total petroleum consumption. The worldwide 

demand for petroleum and its products is now 

doubling about every 10 years. Over the next 
15 years, man is expected to consume as much 

or more petroleum than in the entire previous 

116-year history of the industry. 

Though land areas will continue to attract 

exploration for years to come, current emphasis 

is on the offshore areas for substantial new 

sources of petroleum. The purpose of this report is to review the scope of the offshore 

petroleum search now in progress around the 

world, to present the geographic distribution 

and magnitude of the petroleum found to date, 

to review the time factors involved in the exploration and development of offshore fields, 

and to summarize the geologic characteristics 

of the major offshore producing areas. No attempt is made to provide a descriptive step-bystep history of development nor to present a detailed geologic and technologic analysis, but 

rather to examine the factors that have influenced development to date and that might 

affect future predictions and expectations. 

SCOPE OF THE SEARCH 

Exploration for petroleum beneath the 

world's oceans and seas is in progress on parts 

of the submerged margins of every continent 

except Antarctica. Investigations are being carried out as far south as the Straits of Magellan 

near the southern tip of South America, at approximately 53° S. lat, and as far north as the 

arctic islands of North America, at approximately 80° N. lat. Efforts to date have been 

carried out primarily on that part of the continental margin known as the continental shelf, 

but in some areas exploration is now being extended into the deeper waters over the continental slope and in a few places onto the 

even deeper continental rise. Figure 1 is a map 

showing the various oceans and seas and the 

position of the 2,500-m isobath that approximates the base of the continental slope; figure 

2 is a diagrammatic profile of the continental 

margin, showing average dimensions and the 

terminology applied to the physiographic provinces of the submerged margin. 

The relatively flat-lying continental shelf and 

the more steeply dipping continental slope, 

which together form the continental terrace, 

have a combined area of 55.4 million km2 • Of 

this, about half, or 27.1 million km2 , is occupied by the continental shelf. The continental 

3 

rise, which extends as a gently sloping apron 

from the base of the continental slope to the 

abyssal plain, covers 19.2 million km2

• The 

combined area of the continental margin is 74.6 

million km2 , or about 20.6 percent of the world's 

sea floor, an area about half as large as the 

total land area of the globe. The world's continental margins have not been mapped in the 

detail necessary to give precise areal dimensions; thus the areas given, taken from McKelvey, Stoertz, and Vedder, 1969, are best approximations. 

Offshore exploration during 1972 was in 

progress on the continental shelves and slopes 

of 80 countries and involved 134 companies 

(Wagner, 1972). Some 400 drilling units were 

operating on the continental shelves of 70 

countries (McCaslin, 1972, p. 106) and, at the 

end of 1972, commercial production was reported from 26 countries. Discoveries have 

been made, but development has not as yet progressed to production, off the shores of 15 additional countries. 

The extent of licensing, concessions granted, 

and areas under exploration for the various 

parts of the world are shown in figure 3. The 

figures on the map indicate the number of 

petroleum companies involved in specific concession areas. Where no numbers are shown, 

that information was not available. Some 40 

countries have issued licenses for- exploration 

in water depths greater than 200 m, several to 

depths greater than 2,000 m. Most of the licenses for exploration in water depth in excess 

of 200 m have been granted within the past 

2 years. 

The total number of offshore exploratory 

holes and wells drilled to date around the world 

could not be obtained, although in the United 

States alone the total number of offshore holes 

drilled is approximately 16,000. The approximate number of wells that have produced from 

offshore areas around the world as of December 31, 1972, is 17,400 (Weber, 1972). The 

largest percentage of offshore producing wells 

is in the northern Gulf of Mexico and in Lake 

Maracaibo, Venezuela. Most offshore wells ar·e 

in water depths less than 70 m, but recent 

trends are carrying exploration into deeper 

water, and successful oil wells have been drilled 

in water more than 400 m deep. 
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FIGURE 1.-World map (Mercator projection) showing oceans and seas and generaliz,ed position of the 2,500-m isobath (dashed line). 
Land Ocean 

~ Shelf edge 

0.1° 130m 

Continental 

shelf 

4.3° 

slope 

l-+--- 65km 15-80 km~ 

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4,000m 

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Continental terrace Continental rise Deep sea bed 

Continental margin 

FIGURE 2.-Profile of the continental margin. Numbers shown are worldwide averages. From McKelvey, Stoertz, 

and Vedder ( 1969). 

Drilling companies of the United States are 

involved on a worldwide scale. The current disposition of mobile drilling rigs owned by companies of the United States is shown on figure 

4; of the total, 68 are operating in waters off 

the United States and 122 are working off the 

coasts of other countries. 

RESULTS OF EXPLORATION 

NUMBER AND GEOGRAPHIC DISTRIBUTION 

OF FIELDS DISCOVERED 

Some 780 oil and gas fields had been discovered on the submerged continental margins of 

the world by early 1973. Of that total, 493 

fields are listed as oil and 287 as gas. These 

5 

figures must be qualified as provisional and incomplete because most reporting media have 

only recently begun to separate offshore data 

from total petroleum statistics. Consequently, 

for the several categories of information-wells 

drilled, reserves, and production-the data now 

available for some offshore areas are still somewhat ambiguous; for others they are incomplete; and for a few, no data are available. An 

accurate compilation of the number of gas fields 

is almost impossible to derive because many 

fields produce both oil and gas. In some areas, 

such as the Persian Gulf, gas is flared and is 

neither reported as a reserve nor as production. For oil fields in general, accurate counts 

are difficult to establish because in early stages 
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FIGURE 3.-Generalized offshore areas under concession for exploration worldwide (shaded). Ruled pattern indicates areas under exploration by nationally owned companies. Figures indicate number of companies holding licenses within the specified segment of the offshore-not known for 

some areas. The concessions, licensed areas, and other areas of exploration have been compiled largely from Wagner (1972). 
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FIGURE 4.-Disposition of offshore drilling rigs owned by United States companies. Figures indicate number of rigs operating in specified areas 

(Ocean Industry, 1972). 
of discovery, pools and fields may be reported 

indiscriminately. 

Of the oil and gas fields discovered in the offshore areas, 70 are classified as giants. Sixty 

of these giants are classified as oil and ten as 

gas fields, although eight of them produce both 

oil and gas. Some of these produce from onshore 

as well as offshore. The geographic location of 

the giant fields is shown on figure 5. As used 

in this report, a giant oil field is one containing more than 500 million barrels of estimated 

recoverable oil ; a giant gas field is one containing more than 3,500 billion ft 3 of estimated 

recoverable gas. (This definition of "giant" 

coincides with that used by Halbouty, 1970, p. 

5). 

In this report, the data on the offshore oil 

and gas fi.elds comes primarily from Halbouty 

( 1970) , Weber ( 1972), and Albers and others 

(1973). Use of the term "field" in referring to 

petroleum-producing units and of the names 

applied to them is based on the published identification of others. (See Halbouty, 1970, p. 5, 

504.) 

The distribution of the world's offshore oil 

and gas fields as well as a listing of other discoveries made but not yet developed to production are shown on table 1. 

TABLE 1.-Numbers of offshore oil and gas fields listed 

by continent and country 

[*, indicates discovery but no field development as yet] 

Location 

Africa 

Angola-Cabinda --------- * Cameroun --------------- Congo (Brazzaville) -----

* Dahomey ---------------- Egypt -------------------

Gabon ------------------- * Ghana ------------------- * Libya (gas) -------------

Nigeria 1 ---------------- * South Africa (gas) ______ _ 

* Tunisia (oil) ------------ * Zaire (oil) --------------

Total ----------------

Asia 

Middle East : 2 

Abu Dhabi ------------

Dubai -----------------

Iran ------------------ Iran-Saudi Arabia ____ _ 

Qatar ----------------- * Ras al Khaimah (oil) __ 

Saudi Arabia ---------- Saudi Arabia-Kuwait 

Neutral Zone --------

Numbers of offshore fields 

Giant fields 

Oil Gas 

1 

3 

2 

7 

3 

2 

7 

1 

2 

5 1 

2 

Other fields 

Oil Gas 

4 1 

13 6 

31 

49 7 

5 

5 

2 

3 

1 1 

8 

TABLE 1.-Numbers of offshore oil and gas fields listed 

by continent and country-Continued 

Numbers of offshore fields 

Location Giant fields Other fields 

Oil Gas Oil Gas 

Far East: Indonesia -------------- 19 Japan ----------------- 3 3 

Malaysia-Brunei 1 6 Malaysia-Sarawak 2 

* Papua-New Guinea (gas) 

Total --------------- 23 46 

Europe Denmark ---------------- 6 2 Italy -------------------- 1 20 

* Ireland ------------------ Netherlands ------------- 1 11 

Norway ----------------- 4 2 1 4 1 

* Spain ------------------- 1 United Kingdom --------- 4 4 9 19 

U.S.S.R. ---------------- 2 11 

* West Germany ----------

Total ---------------- 8 5 33 53 

North America 

* Canada (Atlantic Shelf) - Mexico ------------------ 2 14 United States ------------ 7 5276 5 202 

Total ---------------- 9 290 202 

Oceania Australia ---------------- 4 8 

New Zealand ------------

Total ---------------- 4 4 8 

South America Caribbean: 

Trinidad-Tobago ------- 2 6 Venezuela ------------- 69 

Other South America: 

* Argentina 7 ------------ Brazil ----------------- .. Ecuador --------------- Peru ------------------ 5 

Total ---------------- 9 11 6 

Total (Worldwide) -- 60 10 435 277 

1 Sizable gas reserves but not reported by field. 2 Sizable gas reserves associated with oil but unreported separately 

by field. 

a Three others are onshore-offshore. 4 Sizable gas reserves associated with Ekofisk Field. s Approximate because tabulation not available hy fielrl for Gulf of Mexico, where most of the fields are located. 6 Five are offshore extensions of onshore fields. 7 Offshore extensions of Golfo de San J01·ge n•ported but no information available. 

For an additional 22 countries, exploratory 

drilling offshore until January 1, 1972, had 

failed to yield discoveries of petroleum. These 

are shown in the list below by continent and 

region. Included in the list are five countries 

where noncommercial petroleum has been 

found. Sources of the drilling data used in compiling the list are the annual summaries of 

foreign developments in the "Bulletin of the 

American Association of Petroleum Geologists," 

1960 through 1972. 
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FIGURE 5.-World's giant oil and gas fields relative to generalized orogenic belts. Active belts (s•tippled); belts inactive since Paleozoic and Mesozoic 

times (unpatterned); regions not subjected to orogenic movements since Precambrian time (shaded). Solid circles are giant oil fields; open circles 

are giant gas fields; X indicates general areas of disc,overy either of less than giant size or areas under field development. Figures indicate the 

number of field s in a specified area. Adapted from Drake (1972). 
Location 

Africa: 

West Africa : 

Congo, Republic of -------------- Equatorial Guinea ---------------

Liberia ------------------------- Mauritania ---------------------

Morocco1 ----------------------- Portuguese Guinea --------------

Senegal -------------------------

Span~h Sahara ----------------- East Africa: 

Ethiopia ------------------------ Malagasy Mozambique ----------------------- _______ --- __________ _ 

Sudan -------------------------- Asia: 

Middle East: 

Turkey ------------------------- Israel -------------------------- Far East: 

India

1 -------------------------- Phillipines (two wells) ----------

Thailand (one well) ------------- West Malaysia, including central 

part of South China Sea. 

Central America and Caribbean: 

Columbia -------------------------

Honduras ------------------------- Nicaragua ------------------------ Europe: 

France --------------------------- Greece2 --------------------------- Malta ---------------------------- Yugoslavia 2 ----------------------

South America: 

Guyana 3 --------------------------

Surinam -------------------------- 1 Show of oil. 2 Show of oil and gas. 3 Show of hydrocarbon. 

Year of Initial 

Drilling 

1966 

1968 

1971 

1969 

1969 

1968 

1966 

1966 

1965 

1970 

1969 

Prior to 1964 

1970 

1970 

1971 

1971 

1971 

1970 

1971 

1971 

1966 

1972 

1971 

1971 

1971 

1967 

1965 

The countries without significant offshore 

discoveries to date share a common characteristic. With the exception of Colombia, none has 

had previous significant petroleum production 

on land and, without exception, there has been 

little or no production from their onshore 

coastal areas near the continental shelves, The 

most recent licenses issued by some countries 

in this group have been for exploration farther 

out on their continental margins in water 

depths greater than 200 m, indicating that industry interests are shifting farther seaward 

with the hope of finding oil and gas beneath 

the outer part of the continental margin. 

CHRONOLOGY OF OFFSHORE DISCOVERIES 

Considering the exponential growth rate in 

the worldwide demand for petroleum and the 

belief that the offshore must be looked to as 

a large potential future source of petroleum, it 

is important in establishing expectations for 

the future to know what the overall success 

has been in finding new fields and how much 

10 

time is involved in locating a field in a new 

area and subsequently bringing it to production. 

Several factors have strongly influenced the 

rates of discovery and development of petroleum offshore during the period beginning in 

1947. These factors are (1) technical capability, including exploration techniques and engineering methods for drilling, producing, and 

transporting the petroleum from offshore, (2) 

onshore oil production adjacent to the offshore 

area, (3) local physical environmental conditions which include sea-floor topography, water 

depth, sea state, and climate, ( 4) political and 

legal circumstances, including boundaries of 

proprietorship, regulations, and attitudes for 

granting licenses, concessions, and leases, attitudes toward environmental effects, and attitudes about the petroleum company ownership, and (5) capital available for investment. 

Obviously, geologic conditions and, to a degree, long-term patterns of environmental conditions do not vary with time, although they 

vary considerably from place to place. The finding of petroleum as a function of geologic conditions and the production of petroleum found 

in a given environmental situation, whether 

offshore or on land, are directly dependent upon 

man's scientific and technical ability and upon 

economic circumstances at the time. The extent to which exploration and production are 

allowed depends on political attitudes that are 

both national and international in scope and 

not predictable on either a short- or long-term 

basis. Long-term demands may override political considerations, but even this is not a completely valid assumption. 

Available data are not sufficient to permit 

the tabulation of the chronology for the discovery of all 780 fields. However, the discovery 

record for the 70 fields now reported as giants 

is reasonably well known, and figure 6 has been 

prepared showing the distribution of 65 of these 

fields on a time basis during the past 25 years. 

As the giants contain most of the known offshore petroleum, the rate of their discovery provides a good gauge of the success in offshore 

exploration to date. 

The pattern shown by the chart reveals a 

low discovery rate for the years prior to 1957 

and an increased rate of discovery after 1962. 

The low rate of discovery prior to 1957 re-
1971 

1961 ----· Nill., .. 

2 

1959 

1956 

1955 * 

1954 

1953 

1952 

1951-· 1 

1950-·1 

1949 Rli!Dii 2 

1948-

1947- Initial Offshore discovery from mobile platform, Ship 

Shoal, 12 miles (3.6 km) off Louisiana, U.S.A. 

*Year of first offshore wildcat in Eastern Hemisphere, Matbakh 

No.1 off Clatar in the Persian Gulf (Heater, 1956, p. 1647). 

FIGURE 6.-Chronology of discovery of offshore giant 

oil and gas fields. Figures indicate number of fields 

discovered during the specified year. Excluded are 

the onshore-offshore fields of the Venezuela Bolivar 

coastal group for which the offshore discovery dates 

could not be obtained. 

11 

fleets the limited geophysical and drilling capability for work offshore. Offshore geophysical 

exploration techniques and drilling and production ability have been improved considerably 

since the late 1950's. Though not indicated by 

the chart, geologic knowledge gained in petroleum-producing areas locally adjacent to the 

continental shelves has profoundly affected the 

rate and pattern of discovery offshore. The 

search for offshore petroleum began in areas 

having established production along the adjacent shoreline, where geologic conditions governing the petroleum occurrences were known, 

and those regions have the largest number of 

offshore fields. According to Klemm (1971a) 

nearly one-third of all producing basins involve 

some offshore production, and 60 percent represent extension of established onshore production. The offshore giants may be categorized on 

the basis of available data as follows: 22 percent are direct offshore extensions of fields 

that were first discovered onshore, 56 percent 

have geologic conditions that relate closely to 

the producing areas onshore, and 22 percent 

are in geologic settings either not related closely to a petroleum-producing area onshore or 

not predictable on the basis of onshore geology. 

Thus, of the 70 major finds in the offshore to 

date, some 78 percent are in geologic settings 

that are related closely to known onshore conditions. All the offshore extensions were discovered before 1965, and all those not related closely geologically to the onshore have been discovered since 1964. 

In the face of the rapidly rising demand for 

petroleum, the amount of time involved in the 

discovery and development of a commercial field 

offshore has a direct bearing on predicting both 

the short-term and long-range impact of offshore petroleum on future energy supplies. 

The offshore giants have been examined in 

this report in terms of time elapsed between 

the beginning of geophysical explorations and 

eventual discovery and in subsequent development to an initial stage of significant production, defined for the purpose of this analysis as 

at least 1 million barrels per year. The discovery and development time frame for the 

giants has been averaged and is shown in table 

2 in three categories based on extent of prior 

geologic knowledge. For excellent summaries of 

trends in basin development and of the rela-
TABLE 2.-Discovery and development time, in years, 

for the giant offshore petroleum fields 

[Discovery time, from initial geophysical exploration. Development 

time, from discovery to production rate of 1 million barrels per year. Figures in parentheses indicate range of data. Data not 

complete for all fields] 

Extent of previous 

geologic knowledge 

Offshore extension of producing on- shore field, excluding Lake Mara- caibo (7 fields). 

Offshore geology related to that of onshore producing area (25 fields). 

Offshore geology not closely related to onshore producing area (7 

fields). 

Average time lapse 

Discov- Dis- Develop- ery plus covery ment development 

4.4 3.0 7.4 

(2-8) (1-6) 

6.4 2.6 9.0 (1--12) (1-4) 

6.4 4.1 10.5 

(4-10) (3-6) 

tion of giant fields to basin types, reference to 

Klemme ( 1971a-d) is suggested. 

As dates for the beginning of exploration 

could not be obtained in many cases, only 56 

percent of the giant fields could be included in 

the summary shown in table 2. Furthermore, 

as information on the time expended in exploration and discovery of most of the many 

fields of less than giant size is not available, the 

averages indicated are meaningful only as a 

general resume. Also, in considering the time 

required for offshore development, it must be 

remembered that technical capability has grown 

with increasing experience in offshore exploration and development. This probably will continue in the future and could, to some degree, 

shorten the overall time required to find and 

develop. Factors that cannot be accounted for 

in any extrapolations of a future discoveryproduction time frame for the offshore are the 

geologic subtleties that must be accurately interpreted, the political constraints that might 

be imposed on development and production, and 

the extent of technical problems that might be 

encountered when exploration and development 

reach into the deeper waters beyond the continental shelves. 

The ranges of time shown in table 2, even 

though they represent incomplete information, 

have been influenced by local circumstances 

which have affected the rate of development. 

The factors that have influenced development 

can best be recognized by a brief description 

of several specific areas. 

In the Persian Gulf area, reserves of petroleum on land are so large that there has not 

been great urgency to proceed with haste in 

12 

developing the offshore. Furthermore, in the 

Persian Gulf, where the overall petroleum potential has been so great and individual fields 

are so large, development and production have 

proceeded rather systematically in response to 

market demands. 

In Nigeria, where a large petroleum potential 

was not identified until the 1960's, exploration 

and development of producing capacity have 

proceeded rapidly both on land and offshore, 

and drilling activity has been intense. The impetus for rapid development has been twofold: 

the market demand for Nigeria's low-sulfur oil, 

and a desire on the part of the government of 

Nigeria to expand and develop its production 

capacity as rapidly as possible. Consequently, 

fields discovered offshore generally have been 

brought to production in periods of 2 to 4 

years. The very rapid development off Nigeria 

adds another factor that will have a long-range 

effect on discovery and production rates, not 

only for Nigeria, but for any area that undergoes initial rapid exploration and development. 

This factor is the increasing difficulty of finding petroleum after the most obvious and accessible structures have been tested. The discovery rate on the shelf off Nigeria has fallen 

rapidly in the past several years from 85 percent in 1967 to 14 percent in 1971. Exploitation of the Nigerian Continental Shelf has been 

rapid because physical constraints have been 

minimal, production to date has come from 

fields in relatively shallow water, and demand 

for its low-sulfur oil is high. 

In the North Sea, other circumstances have 

prevailed, and the time required for development has been longer. Recognition of the North 

Sea as a potential new source of petroleum 

came with the onshore discoveries of gas at 

Groningen in the late 1950's. Geophysical exploration of the offshore followed soon thereafter, but drilling was delayed until 1964 when 

jurisdictions of the various countries bordering 

the North Sea were established and boundaries 

of proprietorship drawn. The time expended in 

the development of the North Sea as a petroleum province has been influenced principally by 

two factors: geological interpretations that 

guided initial selection of sites for detailed investigation and drilling, and the rigorous physical conditions at sea. Though the Groningen dis-
coveries suggested an offshore potential, the 

North Sea presented a frontier in terms of 

geologic knowledge. In the early stages of exploration, effort was directed to the southern 

periphery of the basin nearest areas of known 

geologic conditions. Not until the late 1960's 

was exploration directed to the central part of 

the basin where the large oil discoveries have 

been made. Thus, initial geologic interpretations prior to exploratory drilling within a 

prospective offshore province can affect the 

time between exploration and discovery. The 

stormy North Sea has given the oil industry 

its greatest test in grappling with severe physical conditions. Rigs and platforms must be built 

to withstand possible wave heights of 100 feet 

(30 m). Consequently, platforms must be built 

that can withstand an overturning force exerted by waves and currents that is 10 times 

greater than that exerted on platforms in the 

Gulf of Mexico. A comparison of sea-state conditions in the northern North Sea with those 

of other offshore areas and the effect of sea 

state on downtime in both drilling and supply 

operations is shown in figure 7, taken from 

AREA 

SANTA BARBARA 

CHANNEL 

GULF OF MEXICO 

EAST COAST 

CANADA 

GULF OF ALASKA 

NORTHERN NORTH 

SEA 

WATER DEPTHS 

OF 450-500 FT 

MAXIMUM WAVE 

HEIGHT, FEET 

Taylor (1973, p. 62). Exploration and development drilling under rigorous North Sea conditions is both long and costly and has put a 

drain on investment capital. The time from initial discovery to anticipated production in 1974 

from the Forties field in the south-central part 

of the North Sea will have been 10 years. The 

Forties field was one of the first two giants discovered in the North Sea. Table 3, gives an 

industry summary of the time required and 

cost for finding and developing a large oil field 

in the North Sea. 

The United States Continental Shelf in the 

Gulf of Mexico has had the greatest concentration of exploration and drilling and by far the 

largest number of producing fields of any offshore area in the world. Even there, precise 

data on the time required to discover and produce from a given field is difficult to obtain. 

Consensus from a variety of sources seems to 

be that the average time required to bring a 

field to significant production after initial discovery has been 1-3 years. When account is 

taken of the time devoted to exploratory drilling, the elapsed time from granting of leases 

DRILLING 

OPERATIONS 

DOWNTIME, 

PERCENT 

SUPPLY 

OPERATIONS 

DOWNTIME, 

PERCENT 

FIGURE 7.-Comparison of sea-state conditions in selected offshore areas and the effect on drilling and supply 

operations. From Taylor (1973). 

13 
TABLE 3.-Time span and costs for finding and developing an oil field in the North Sea 

[Field size, 1 billion barrels recoverable reserv~s and 250,0~0 barr,..els per day capacity. Adapted from Petroleum Press Service, 1912, 

p. 410] 

Direct Capital Operating 

Time employ- invest- expendi-

(years) ment ment ture (men) (millions) (millions) 

Exploration: 2,000- 1 2-6 200-400 $24-147 

4,000 km of geo- physical surveys, 5-30 explorationappraisal wells. 

Construction : plan- 1 5-6 1,000-2,000 $612 

ning design, pro- duction well drill- ing, production and transport facilities. 

Production ---------- 2 16-20 300-400 3$122-245 $612-735 

1 Overall range for exploration and construction, 7-12 years. 2 Includes buildup, 3-5 years; plateau, 5 yP.ars; and decline, 8-10 

ye:~~pendent on type of secondary recovery scheme or other operation necessary. 

to production of petroleum has generally been 

3-4 years. After the December 1972 lease sale 

in the Gulf of Mexico, which included blocks on 

the outer part of the continental shelf in water 

depths ranging from 250 to 425 feet (76-129 

m), industry sources forecast that significant 

production from these leases could be expected 

in 4-5 years (Ocean Industry, 1973). 

The principal determining factor in the time 

required to find and produce from a new concession is how soon the initial significant discovery will be made, a factor that relates in 

part to how the geology of the prospect has 

been interpreted. The time span for finding 

new fields on the continental shelf in the Gulf 

of Mexico would be expected to be relatively 

short because the northern continental shelf of 

the gulf is a salt-dome province, and the nature 

of the targets is reasonably well understood. 

As the search moves away from the area of 

such obvious targets to other areas of the gulf, 

such as the carbonate banks of the Florida 

shelf, more subtle geologic conditions may be 

found that could change the time required for 

discovery and development. 

Obviously, the time involved in finding and 

producing petroleum offshore results from a 

composite of circumstances, each of which may 

vary in degree of influence from one area to 

another. Consequently, it is not possible to 

correlate directly from area to area the time 

required to find and produce petroleum purely 

on the basis of past experience. Nevertheless, 

one can make the generalization that in areas 

14 

such as the Gulf of Mexico salt-dome province, 

offshore Nigeria, and the Persian Gulf where 

the potential is large and the nature of the 

geological targets is reasonably well understood, new discoveries can be made and brought 

to production within a time span of 3-4 years. 

For areas such as the North Sea, where the 

potential is large but physical conditions of the 

environment are a limiting factor, a reasonable 

expected time span from granting of a concession to significant production is 7-12 years. 

Assuming that the next few years will bring 

a concerted effort to find new sources of petroleum offshore, how soon can the United States 

expect to have substantially increased production to help meet its large and growing domestic 

demand? Outside the Gulf of Mexico, the obvious prospects for large future offshore efforts 

are the Atlantic continental margin, southern 

California, Alaskan waters including the Gulf 

of Alaska, the Bering Sea, the Chukchi Sea, 

and the Beaufort Sea shelf off northern Alaska, 

and Prudhoe Bay. 

Because of its proximity to the large population and industrial centers of the eastern part 

of the country, the Atlantic continental margin 

of the Eastern United States is receiving increased attention as a possible new source of 

petroleum. Offshore geophysical exploration on 

the Atlantic Continental Shelf began some 10 

years ago, and over the past 8 years considerable geophysical work has been done on that 

part of the shelf north of Cape Hatteras. How 

soon could we expect production from the northeastern United States Atlantic Continental 

Shelf if the decision to drill is made in the 

reasonably near future? The Atlantic Continental Shelf has not been drilled for oil and gas, 

and its onshore extension, the Atlantic Coastal 

Plain from southern Florida to New Jersey, 

has yielded no significant shows of petroleum 

from the scattered drilling that has been done 

all along the coast over the past several decades. Because it falls in the category of those 

offshore areas around the world with no history 

of adjacent onland petroleum production, its 

petroleum potential cannot be judged accurately from geologic ~onditions that exist along the 

coast. However, sedimentary rocks along the 

shoreline are known to thicken seaward beneath the shelf and reach thicknesses of more 
than 5,000 m along parts of the outer edge of 

the continental shelf and farther out beneath 

parts of the continental slope and rise (Maher, 

1971, p. 4). If petroleum is present in commercial quantities, the time lapse from granting of leases to discovery will depend upon the 

accuracy of initial geological interpretations in 

picking targets for initial exploratory drilling. 

Assuming reasonably early discovery after exploration drilling begins, development and production will encounter physical conditions at 

sea that will range regionally from somewhat 

more rigorous than those in the Gulf of Mexico 

to those that will at times approach conditions 

typical of the North Sea on the northern part 

of Georges Bank. A reasonable time lapse from 

discovery to significant production probably 

would be in the range of 6-10 years, the actual 

time required to produce depending on where 

and beneath what depths of water petroleum 

might be found. As for the Gulf of Alaska, 

where sea states are virtually analogous to those 

of the North Sea and where climatic conditions 

are harsh, significant production could be estimated somewhere within the range of 8-12 

years depending on early discovery after initial drilling starts. 

Speaking from a high-level industry viewpoint, the Chairman of the Board of the Exxon 

Company, U.S.A., remarked recently in the 

August 1973 issue of the Exxon publication 

"The Lamp" that the United States could not 

expect significant production from either the 

Atlantic Continental Shelf or the Gulf of 

Alaska in this decade. 

Several of the factors that influence the time 

required to find and produce new sources of 

petroleum from the offshore in areas not previously tested by drilling can be expected to 

change, and these changes will affect the time 

required to produce. The ability to complete 

and maintain wells from units placed directly 

on the sea floor will reduce the time required 

to carry out development drilling not only in 

areas of heavy sea states, such as the North Sea, 

but in other areas as well. Planning and development of sea-floor completion systems has 

been underway for some years, and four known 

subsea tests are also underway (Bleakley, 

1973). One of these has been in successful operation since October 1972, in 375 feet (114m) 

15 

of water in the Gulf of Mexico (Taylor, 1973; 

Bleakley, 1973). Testing of a sea-floor system 

in the North Sea is planned for the near future. 

However, some of the time that will be saved 

by use of sea-floor completion systems may well 

be offset as exploration moves further into new 

areas of the offshore where the geologic conditions are less well known. The current trend 

into areas less well known is, as has been mentioned, taking the search into deeper water 

where exploration times will be 1onger and engineering costs much higher, placing a heavier 

burden on capital available for investment. 

Weighing both the multiple factors involved 

and their varying interplays from place to 

place, the time required to produce after initial discovery in frontier areas will likely remain 2-5 years for those areas that are in water 

depths of less than 300 feet (91 m) and will be 

in the range of 7-14 years for those that are 

in water more than 400 feet (121 m) deep. 

No attempt has been made to summarize the 

costs and economics of offshore development 

because data are not readily available and thus 

are too incomplete to permit a definitive discussion. However, the estimated development 

cost for the Ekofisk field complex in the North 

Sea is $1.5 billion (Oil and Gas Jour., 1972, p. 

33) . This estimate is based on a water depth 

of less than 85 m. The estimate does not include higher costs of development that will be 

encountered for those parts of the Ekofisk field 

complex that are farther out in depths of 200 

m and more. The cost of laying a crude-oil 

and condensate pipeline from the Ekofisk field 

to the United Kingdom, a distance of some 320 

km, is estimated to be $200 million (Oil and 

Gas Jour., 1972, p. 45). Although the costs 

just discussed are for a specific situation that 

may not apply generally, they reflect the high 

costs involved in developing new large fields in 

frontier areas of exploration where physical 

conditions are rigorous. 

In summarizing the economics of offshore 

production, the comments of Weeks (1973a) 

are pertinent to the general trend that might 

be expected in the future. He stated, p. 17, 

"studies show that costs of exploitation increase at an exceedingly rapid rate with increasing water depth; for example at 330 m 
the cost will be at least four times higher than 

at 33 m, where the cost is already twice that 

of an on-shore field of similar characteristics. 

Operations under 330 m or more of water may 

be so costly that only giant fields will perhaps 

be profitably exploited . . . Distance from 

shore will also influence the economic possibilities of developing offshore fields, particularly 

in the case of natural gas, as there are no viable 

alternatives for transporting to shore installations other than by pipeline." 

OFFSHORE PETROLEUM RESERVES AND 

PRODUCTION 

The current status of the worldwide search 

for petroleum offshore and its success are revealed best by examination of the production 

and reserves figures for those areas where exploration and development have progressed to 

the point that production has become substantial and reserves can be estimated with reasonable accuracy. The geographic distribution and 

the magnitude of offshore oil production and reserves by continent and country to January 1, 

1973, are shown in table 4; production and reserves of natural gas to January 1, 1972, are 

shown in table 5. The giant fields are listed by 

name. The reserves and production figures for 

the tables have been taken largely from vVeber 

(1972) and from Albers and others (1973). 

The production figures for 1972 that have been 

included in the cumulative production figures 

in table 4 were taken from McCaslin (1973a). 

The tables are provisional for several reasons. Only in the past 2 years have offshore statistics begun to be reported separately from 

total production in some of the reporting media. 

Consequently, ambiguities and inconsistencies 

exist in both production and reserves statistics 

reported for some of the fields in the Gulf of 

Mexico and for some of the fields that straddle 

the shoreline and produce from both onshore 

and offshore. Furthermore, some of the estimates of reserves are not available for some 

fields of less than giant size, as indicated in the 

tables. Nevertheless, in all cases, the reserve 

estimates tabulated are based on some drilling, 

not broad favorability factors, and, therefore, 

are essentially measured reserves. 

The reserve and production figures listed in 

tables 4 and 5 are somewhat less than the 

16 

TABLE 4.-Provisional estimated recoveralJle reserves, 

in millions of barrels, and cumulative production offshore 

[Giant fields indicated by name. Parentheses indicate figure esti- mated from initial drilling. NA, not available. SI, shut in, not producing. X, field partly onshore] 

Location, field, and year discovered 

A/Tica 

Angola-Cabinda: 

Cabinda "B," 1966 -------------

Other ( 1 field) ----------------- Congo (Brazzaville), Emeraude 

Marine, 1969 ------------------ Egypt: 

Amal, 1968 -------------------- El Morgan, 1965 ---------------- Helayim Marine, X, 19til ~-----­

Other (4 fields) --------------- Gabon (13 fields) ---------------- Nigeria: 

Meren, 1965 ------------------- Okan, 1964 -------------------- Other (31) ---------------------

Total ----------------------

Asia Middle East : Abu Dhabi: 

Mubarras, 1969 -------------- Umm Shaif, 1958 ------------

Zakum, 1964 ----------------- Other (6 fields) -------------- Dubai: 

Fateh, 1966 ------------------ Fateh, SW, 1970 ------------- Iran: 

Bahrgansar, 1960 ------------

Cyrus, 1962 ------------------ Darius, X, 1961 -------------- Henijan 2, 1968 -------------- Nowrouz, 1966 --------------- Sassan, 1966 ----------------- Rostam, 1967 ---------------- Other (5 fields) -------------- Iran-Saudi Arabia, FereidoonMarjan, 1966 ---'------------- Qatar: 

Idd-el-Shargi, 1960 ----------- Maydan-Mahzam, 1963 ------- Saudi Arabia: 

Berri 4, X, 1964 ------------ Safaniya X, 3 1951 -----------

Manifa X, 1957 -------------- Qatif X, 3 1964 --------------- Abu Sa'fah, 1963 ------------ Other (3 fields) -------------- Saudi Arabia-Kuwait Neutral Zone: 

Kahfi,4 1960 ----------------- Hout, 1969 ------------------- Other (1 field) ---------------

Middle East subtotal -------------

Far East: Malaysia-Brunei: 

Ampa, SW, 1963 ------------- Other (6 fields) -------------- Malaysia-Sarawak (2 fields) __ _ 

Indonesia (10 fields -----------

Japan ------------------------- Far East subtotal ----------------

Total ----------------------

EuTope 

Norway: 

Ekofisk, 1970 ------------------- Edda, 1972 --------------------- Other ( 4 fields) ---------------- United Kingdom: 

Brent, 1972 -------------------- Forties, 1970 ------------------ Comorant, 1972 ----------------

Halibut, 1972 ------------------

Other (9 fields) ---------------- Denmark (6 fields) -------------- Netherlands (1 field) ------------

Italy (1 field) -------------------- Spain (1 field) ------------------

See footnotes at end of table. 

Cumu- Estimated lative recover- produc- Estimated 

able tion remaining 

reserves to 111/73 reserves 

1,230 127 1,103 

NA NA NA 

500 499 

2,500 0 2,500 

780 381 399 1,400 225 1,175 

NA NA NA 1,100 68 1,032 

628 113 515 

588 166 422 1,295 236 1,059 

10,021 1,317 8,704 

2,000 0 2,000 2.223 328 1,895 

1,257 339 918 NA 0 NA 

1,581 128 1,453 1 (500) 0 1 (500) 

1,039 85 954 

814 30 784 1,334 250 1,084 

454 17 437 969 24 945 

1,467 204 1,263 

1,000 56 944 

NA NA NA 

10,000 0 10,000 

2,115 123 1,992 

10,249 303 9,946 

5,926 223 5,703 

25,377 2,307 23,070 

11,010 98 10,912 

9,039 375 8,664 

6,529 166 6,363 

NA NA NA 

1,734 952 782 

998 70 928 

NA NA NA 

97,615 6,078 91,537 

2,a41 178 2,163 

689 82 607 5200 NA 5 200 5400 27 5373 

24 9 15 3,654 296 3,358 

101,269 6,374 94,895 

3,010 13 2,997 

(500) 0 (500) 

NA NA NA 

(1,000) 0 (1,000) 

4,400 0 4,400 

(1,000) 0 (1,000) 

NA (Industry places in giant class) 

NA NA NA NA SI NA NA NA NA 152 66 86 

150 0 150 
TABLE 4.-Provisional estimated 'recoverable rese1·ves, 

in million of barrels, and cumulative production offshore-Continued 

Location, field, and year discovered 

U.S.S.R.: 

Estimated 

recoverable reserves 

Sangachaly-Duvannyi-Bulla, 1963 1,036 

Neftyanye---Kamni, 1949 ------- 1,260 

Other (11 fields) --------------- NA 

Cumulative 

production to 1/1/73 

100 

760 

NA 

Estimated 

remaining 

reserves 

936 

500 

NA 

---------------------- Total ---------------------- 12,508 

North America 

Mexico: 

Arenque, 1967 ------------------

Atun, 1966 --------------------- Other (14 fields) --------------- United States: Louisiana: 

West Delta Blk. 73, 1962 ----- Bay Marchand Blk. 2, X, 1949_ 

South Pass Blk. 24, 1950 ----- Timbalier Bay, X, (1955-63) __ 

Other (9 fields) G -------------

Other (248 fields) 7 -------------

California: 

Huntington Beach, X, 1962 __ _ 

Wilmington, X, 1964 ---------

Santa Ynez,s 1970 ------------

Other (11 fields) ------------- Texas (2 fields) ---------------- Alaska, Cook inlet (4 fields) ___ _ 

Total 

Oceania 

Australia: 

1,000 

924 

200 

720 

780 

1,072 

651 

2,599 

6,00,0 

501 

1,279 

3,000 

580 

98 

746 

20,150 

Barracouta, 1965 --------------- 502 

Halibut, 1967 ------------------ 645 Kingfish, 1967 ------------------ 1,010 

Marlin, 1966 ------------------- 500 Other (1 field) 9 ---------------- 208 Other (4 fields) ---------------- NA New Zealand (1 field) ------------ 11 

939 11,569 

4 996 25 899 53 147 

111 609 364 416 

340 732 361 290 1,207 1,392 

3,R68 2,132 

415 86 713 566 

0 3,000 

243 337 8 90 328 418 

8,040 12,110 

6 496 152 493 

79 931 NA NA 

68 140 NA NA 1 10 

------------------------- Total ------------------------ 2,876 

Caribbean 

Trinidad-Tobago (1 field) --------

Other (1 field) ----------------- Venezuela: 

Centro, 1957 ------------------- Ceuta, 1957 --------------------

Lama, 1957 -------------------- Lamar, 1958 ------------------- Bolivar Coastal : 

420 

NA 

743 

623 

2,675 

1,841 

Bachaquero, X ---------------} Cabimas. X ------------------ 1115,000 

Lagunillas, X ---------------- Tia Juana, X ---------------- 3,962 Mene Grande, X ------------- 601 

Total ---------------------- 25,865 

10 306 10 2,070 

236 184 NA NA 

282 461 195 428 

1,675 1,000 

593 1,248 

13,591 1,409 

2,672 1,290 573 28 

19,817 6,048 

===================== 

South America (other than Venezuela) 

Argentina ----------------------- NA NA NA 

Brazil --------------------------- NA NA NA 

Peru ---------------------------- 141 51 90 

------------------------- Total (Other than Venezuela) 141 51 90 

===================== Total, (Worldwide) --------- 172,830 1036,844 10 135,486 

1 Fateh, SW reported as giant but reserves not available; figure listed is estimated minimum. 2 Included as giant through reserves slightly less than 500 million barrels. 3 Dates of initial onland discovery. 4 Extension of Safaniya Field. 5 Estimated. 

'

1 Fields with estimated reserves of >100 million barrels at time of discovery. 7 For 34 wells of this group, cumulative production is half of re- serves; this ratio was applied to the reported production for 215 

of the wells (Weber, 1972) to obtain estimate of 6,000 million barrels. 8 Estimate based on single well. 9 Barrow Island Field. 10 Minus figures for Marlin Field, Australia. 11 Total reserve listed for Bolivar Coastal onshore and offshore is 30,000 ; offshore part is estimated to be half of total. 

17 

TABLE 5.-Provisional ·worldwide estimated rec,overable 

offshore gas reserves and cumulative production, in 

b·illions of cubic feet 

[NA, not available. INC, incomplete] 

Location 

Africa: 

Estimated 

recoverable 

reserves 

Cumulative 

production 

to 1/1/72, 

except at noted 

Egypt ------------------- 1 1,000 NA 

Gabon ------------------- 7,000 NA 

Nigeria ----------------- 10,000 NA ------------------------

Total ---------------- 18,000 NA 

Asia, Middle East: 

Saudia Arabia ----------- Kuwait-Neutral Zone ____ _ 

Union of Arab Emirates: 

Abu Dhabi, Dubai, Ras 

al-Khaimah, Umm al-

================= 

14,600 

875 

NA 

37 

Qaiwan, Sharjah, Ajman 2,165 NA ------------------------ Total --------------- 17,640 37 (INC) 

Europe: 

North Sea 2 -------------- 60,000 1,130 

Italy -------------------- 3,530 3 300 ------------------------ Total ---------------- 63,530 1,430 ==================== North America, United States 39,500 20,600 ------------------------ Total --------------- 39,500 20,600 

Oceania: 

Australia ---------------- 20,300 48 

New Zealand _ ------------ 6,000 0 -----------------------

Total --------------- 26,300 48 

Caribbean, Trinidad-Tobago _ 3,500 39 ------------------------

Total --------------- 3,500 39 

Total, (worldwide) --- 168,470 22,154 (INC) 

1 Gas is also produced from the El Morgan Field but the amount 

is not available. 2 Discovery rate in the North Sea has been high during the past year and an accurate breakdown of reserves by country is not 

available. s To 1/1/71. 

actual values because of the lack of statistics 

for a number of fields of less than giant size. 

Nevertheless, it is unlikely that inclusion of 

data not currently available for the smaller 

fields would substantially change the order of 

magnitude of either the worldwide or regional 

totals as shown in the tables, because the 

amounts of reserves for fields of less than giant 

size are small relative to the reserves in the 

giant fields. 

The geographic distribution and magnitude 

of petroleum reserves and production offshore 

relative to onshore reserves and production are 

shown graphically by figure 8. Of the offshore 

oil discovered so far, 56 percent has been found 

in the Persian Gulf, and an additional 14 
1-l 

(X) 

oo 

60 

BILLIONS 

OF TONS 

EXPLANATION 

TOTAL PRODUCTION 

TOTAL RESER YES 

OFFSHORE PRODUCTION 

AND RESER YES 

c:::::> 

~~ ?]D 

0 

Middle East 

goo 

Q 

BILLIONS 

OF BARRELS 

200 

375 

FIGURE 8.-Relation of offshore oil reserves and production to total world oil reserves and production. Adapted from the British Petroleum Co., Ltd. 

(1973). 
percent is reported for Lake Maracaibo, giving 

the two areas 70 percent of the world offshore 

total. The offshore estimated oil reserves, as 

reported in table 4, represent approximately 

26 percent of the world's estimated recoverable 

reserves at this time. 

The giant offshore oil fields contain some 157,-

817 million barrels or about 90 percent of the 

oil reported recoverable for the offshore. In 

terms of estimated recoverable reserves, seven 

of the offshore giants rank among the 20 largest 

oil fields in the world; six are in the Persian 

Gulf. The Safaniya Field, Saudi Arabia, is the 

world's largest offshore field, and it ranks 

second among all oil fields, both onshore and 

offshore. Table 6 shows the ranking of the offshore oil giants among the world's 20 largest 

oil fields. 

TABLE 6.-World's largest oil fields, in billions of barrels 

[*, offshore giants. Principal source, Weber, 1972] 

Rank Production 

Field Amount 

L ___ Kuwait (5+ fields) ------------------- 13.3 

2 ___ *Venezuela (Lagunillas) ---------------- 7.7 

3 ____ Saudi Arabia (Ghawar) --------------- 6.6 

4 ____ Iraq (Kirkuk) ------------------------ 5.6 

5 ____ Iran (Agha Jari) --------------------- 4.8 

6 ____ Venezuela (Bachaguero) --------------- 4.2 

7----U.S.A. (East Texas) ------------------ 4.0 

8 ____ Saudi Arabia (Abqaiq) ---------------- 3.7 

9 ___ *Venezuela (Tia Juana) ---------------- 2.6 

10 ____ Iran (Gach Saran) -------------------- 2.5 

1L __ *Saudi Arabia (Safaniya) -------------- 2.3 

12 ____ Algeria (H. Messaoud) ---------------- 1.66 

13 ____ Iran (Haft Kel) ---------------------- 1.63 

14 ____ U.S.S.R. (B.S.R.) --------------------- 1.6 

15 ___ *Venezuela (Lama) -------------------- 1.6 

16 ____ Libya (Zelten) ----------------------- 1.5 

17 ___ *U.S.A. (California-Wilmington) _______ 1.48 

18 ____ Iraq (Rumaila) ----------------------- 1.4 

19 ____ Indonesia (Minas) -------------------- 1.38 

20 ____ U.S.S.R. (Aliyurt) -------------------- 1.35 

1 Some sources estimate as high as 20 billion. 

In overall production from the offshore, 

Venezuela, the United States, and the countries 

of the northwest Persian Gulf have accounted 

for some 92 percent of the world total. Production rates have been considerably higher in 

Venezuela and the United States than in the 

Persian Gulf, and, consequently, a considerably 

larger percentage of the discovered oil in each 

of these countries has been depleted. Of the 

estimated offshore reserves, some 91,537 million barrels, or approximately 70 percent, are 

in the Persian Gulf. 

Total offshore oil output in 1972 increased 

3.8 percent over 1971 (McCaslin, 1973a, p. 

126). Worldwide production from the offshore 

increased from 2.6 billion barrels in 1970 to 3.3 

billion barrels in 1972 (McCaslin, 1973a, p. 

126) and now accounts for about 17 percent 

of total world production. 

Data are still not sufficient for making either 

a complete estimate of potential subsea petroleum resources or for making a meaningful 

19 

Estimated recoverable reserves 

Field Amount 

Saudi Arabia (Ghawar) ------------------ 75.4 

*Saudi Arabia (Safaniya) ---------------- 25.3 

U.S.S.R. (Samotlorskoye) ----------------- 15.1 

U.S.S.R. (Romashkino) -------------------- 14.3 

Iraq (Rumaila) -------------------------- 12.3 

*Saudi Arabia (Manifa) ------------------ 11.0 

*Venezuela (Lagunillas) ------------------ 10.5 

Iraq (Kirkuk) --------------------------- 10.2 

*Iran-Saudi Arabia (Fereidoon-Marjan) ---- 10.0 

Iran (Marun) ---------------------------- 9.7 

U.S.A. (Prudhoe Bay) ------------------- 1 9.6 

*Saudi Arabia (Qatif) --------------------- 9.0 

Iran (Gach Saran) ----------------------- 8.8 

Saudi Arabia ( Abqaiq) ------------------- 8.6 

Iran (Ahwaz) --------------------------- 8.5 

Libya (Sarir) ---------------------------- 7.7 

Iran (Bibi Hakimeh) --------------------- 7.5 

*Saudi Arabia (Abu Sz'Fah) --------------- 6.5 

U.S.A. (East Texas) --------------------- 6.0 

*Saudi Arabia (Berri) --------------------- 5.9 

revision of Week's 1969 estimate of 700 billion 

barrels, a figure that is based on mass volumes 

of sedimentary rocks and broad geologic favorability factors. In fact, Weeks (1973a) has revised his 1969 estimate to 2,272 billion barrels 

of ultimate potentially rec-overable oil plus oil 

equivalent of the gas. However, with regard to 

the validity of his new estimate, Weeks (p. 13) 

stated, "It should be pointed out that in making this estimate it was assumed that all of 

this petroleum will be economically recoverable. 

This may not be found possible particularly 

with respect to deeper water areas of lower 

average productivity. It must be emphasized that 

such estimates are, at best, speculative and are 

based on industry experience in more mature 

areas having similar geological characteristics. 

The fact that the figures employed are relatively specific should not be interpreted as altering 

their speculative nature." He stated further (p. 

16-17), "Of the total estimated resources of 

2,272 billion barrels, perhaps less than 25 per-
cent are in potentially highly productive areas 

. . . 372 billion barrels of potential petroleum 

resources will be found in highly productive 

areas." 

The world subsea petroleum resource potential is unquestionably large, but the magnitude obviously cannot as yet be accurately defined. Offshore exploration for petroleum, now 

of worldwide scope, is becoming increasingly 

intense in many areas of the world. Results, 

disappointing to date in some areas, have been 

spectacular in others. Over the next few years, 

the worldwide reserves of petroleum will be 

substantially increased, and by the end of the 

next decade, offshore data should be sufficient 

to make significantly improved estimates of 

world subsea petroleum potential. 

For the United States, estimates of offshore 

petroleum potential have ranged from conservative to highly optimistic. For the Gulf of 

Mexico, McCaslin (1972, p. 108), reporting the 

opinion of others, gave a "reasonable potential" 

of 21 billion barrels of oil and 169 trillion ft 3 

of natural gas. The State of California estimates 

its offshore potential to be 30 billion barrels. 

The outer continental shelf waters off California almost certainly have an even larger 

potential. In a report on the energy resources 

of the United States, Theobald, Schweinfurth, 

and Duncan (1972, p. 8-10) estimated that the 

undiscovered petroleum resources of the offshore to the 2,500-m water depth that might 

be found and recovered under approximate 

1972 economic conditions and using existing 

techniques are 200 billion barrels of oil and 

natural gas liquids and 850 trillion ft 3 of natural 

gas. Their estimate was derived by considering 

first the geological favorability of the offshore 

areas and then extrapolating the results of past 

exploration drilling to the remaining unexplored but favorable rocks, following a method 

developed by A. D. Zapp and T. A. Hendricks 

(Hendricks, 1965). 

The future petroleum potential worldwide, including offshore areas, recently has been summarized in a series of four articles by Weeks 

( 1973b-e). Though petroleum resource potential for offshore areas is not listed separately 

from total potential, the four articles are an 

excellent global coverage. His discussions summarize the interplay of reserves, production, 

20 

and mounting demands and what these portend 

for the future of petroleum as an energy source . 

GEOLOGIC SUMl\IARY OF THE WORLD'S 

OFFSHORE PRODUCING AREAS 

Areas of the world's oceans and seas having 

geologic conditions generally favorable for the 

occurrence of petroleum are portrayed on sheet 

three of the McKelvey and Wang report of 1970. 

However, as pointed out in their report and as 

indicated in the foregoing summaries of this 

report, conditions considered most favorable for 

petroleum are highly localized, and exploration 

efforts, though geographically extensive, have 

become more concentrated in those areas where 

initial exploration and ensuing discoveries have 

indicated a high potential. No attempt is made 

here to describe in detail the geologic conditions in the specific producing areas but rather 

to summarize the geologic characteristics of the 

areas containing giant petroleum fields. 

The most favorable habitat of petroleum offshore, as onshore, is the sedimentary basin and 

in particular those basins where sediments 

have accumulated to a thickness of more than 

1,000 m. Such basins are scattered over all the 

continents but, at the present stage of geologic 

time, tend to be concentrated along the continental margins-the shelf, slope, and rise. 

Large amounts of detritus are eroded from the 

the landmasses and carried to the oceans and 

seas by rivers and deposited in the oceans peripheral to the continents. However, the sizes of 

these basins, their internal geologic structure, 

their tectonic history, and the thickness of 

sedimentary rocks in them vary considerably. 

The general distribution by thickness of sedimentary rocks peripheral to the continents is 

shown by figure 9. The shaded areas on the 

map indicate those areas where the thicknesses 

are more than 3,300 m. Within these areas are 

basins containing sedimentary rocks more than 

7,000 m thick, but because of scale limitations 

no attempt has been made to show these areas 

or to outline specific basins. The formation of 

the basins that through geologic time eventually become habitats for oil is a part of the wide 

scope of tectonic processes that have molded 

the face of the earth as we see it today. The 

genera] tectonic belts of earth, separated on 

the basis of the geologic age, in which various 
r-.:1 

...... 

60 

0 

60 ,....- __ ............. .... --:; 

2,500-m isobath // "~-

proximate base of continental slop~- ,-/ 

FIGURE 9.-Thickness of sedimentary deposits in the submerged continental margins. Stippled areas contain deposits 1,000 to 3,300 m thick; shaded 

areas contain deposits more than 3,300 m thick. Ruled pattern areas represent major deltaic deposits in the submerged continental margin. 

Adapted from booklet, "Deep·water Capabilities" produced by staff of E.sso Production Res·earch Company (1972). 
parts of the crust have been mobile in the past, 

as well as those that are currently in a mobile 

state, are shown in figure 5. 

For a description of the geology of the submerged continental margins of the world, summaries of broad scope by Hedberg (1970), 

Emery (1969), and Klemme (1971a), are recommended for the readers wishing a somewhat 

more detailed overview. Hedberg discusses the 

continental margins from the viewpoint of the 

petroleum geologist, Emery presents a sixfold 

classification of the continental shelves based 

on origin, and Klemme relates the world's basin 

areas to the continental masses and their margins. Both the Hedberg and Emery reports 

point out the limited extent of our knowledge 

about the geology of the submerged margins. 

Emery (p. 108-109) classified the present state 

of knowledge of the continental shelves of the 

world on a map which shows approximately 

65 percent of the total shelf area to be poorly 

known and an additional 20 percent or so as 

moderately known. Hedberg concluded his report with the following observations: 

1. We still have essentially no direct observational information on the nature of the sediments making 

up the continental rise-the most impressive accumulation of sediment on the earth's surface .... 

2. In spite of all our stress on the importance of the 

contact of oceanic crust and continental crust, and 

our dependence on refraction seismography information for its identification, we have extremely 

few adequately detailed continuous refraction surveys across the critical part of the continental 

margin. 

3. Finally, in spite of all our studies of the sediments 

of the past and the sediments of the margins of 

today, we are still largely unable to identify and 

differentiate with assurance in the strata of the 

past the counterpart deposits of slope, rise, marginal, sea, outer shelf, and the other realms of the 

continental margins of today. 

More intensive research is needed urgently if we are 

to understand the nature of the continental margins, 

the crustal processes active there, and their bearing 

on the geology of the past. This information is of importance to all earth science, but is particularly vital 

in the search for petroleum. 

Some years ago, Weeks ( 1952, p. 2096), in 

a discussion of factors that control oil occurrence, proposed a classification of sedimentary 

basins relative to the earth's crustal framework, degree of mobility, and source and type 

of sediments. His classification recognizes two 

22 

major groups: Basins of mobile belts and those 

of relatively stable regions. More recently, 

Klemme (1971a) has elaborated on trends in 

petroleum basin development using the same 

general basic classification as Weeks, but building into his presentation more recent development in knowledge about earth's tectonic processes and in particular new ideas concerning 

basin development and the new concepts of 

global plate tectonics. 

A summary of the geologic characteristics of 

the giant offshore oil fields relative to their 

po~ition within the earth's mobile and stable 

belts, using the basic concepts of Weeks and 

Klemme, is shown in table 7. 

In summary, the overall characteristics of 

the world's offshore giant petroleum fields as 

shown by the table are as follows: 

No. Age of producing horizons of 

fields 

Tertiary ------------------ 25 

Mesozoic ------------------ 32 

Paleozoic ----------------- 4 

Not available ------------- 8 

No. Reservoir type of 

fields 

General carbonates ________ 24 

Sandstone ---------------- 35 

Not available _____________ 10 

Percentage 

of total 

fields 

37 

47 

6 

11 

Percentage 

of total 

fields 

35 

52 

14 

In terms of petroleum occurrence the three 

basin subclasses have the following individual 

characteristics: 

1. The intracratonic basins, which are within 

the continents, contain a total of 19 giant 

fields and 61 fields of other than giant 

size: oil and gas seem to occur in very 

nearly equal proportions, although the 

oil giants outnumber the gas giants. 

2. The intermontane basins, which are within 

those parts of earth's crust that have 

been tectonically mobile in both Tertiary 

and recent times, contain 14 giant oil 

fields, 19 oil fields of other than giant size, 

:tnd only one known gas field; they have 

no known carbonate reservoirs and no 

evaporites that have played a role in petroleum entrapment. 

3. The extracontinental basins, along the periphery of the continents, have a rather 

wide range of geologic settings that make 

the class somewhat arbitrary. 
TABLE 7.-Characteristics of giant offshore petroleum fields relative to geologic setting 

[Fields other than giants shown in parentheses; not all fields shown. Ss, Sandstone. Ls, Limestone. NA, Not available] 

Averages of Evaporites crude oil Pro- significant analyses 

Number of ducing Type factor in 

fields depth Geologic age of petroleum Gravity Sulfur 

ranges of producing reser- concen (degrees (perBasin class and sub-types Geographic location Oil Gas (feet) reservoirs voir tration Baume) cent) 

Stable regions 

Intracraton: Subtype A, intracontinental North Sea --··--------- 6(20) 4(33) 4,500- Permian- Ss. and Yes 36.0 0.16 downwarp. 10,900 Cretaceous. Ls. 1 

Subtype B, graben --------- Gulf of Suez, Red Sea - 3(4) 1 5,500- Miocene Ss. YeR 30.5- 1.67-

9,000 32.0 1.80 Subtype c. half-graben ---- Gippsland basin, 4(2) 2(2) 4,500- Eocene-- Ss. No 41.7- 0.12-

Australia. 8,450 Paleocene. 45.4 0.16 , Total -----------------~------------------------ 13(26) 7(35) 

Mobile regions 

Intermontane: 

Subtype A, Unstable border- California ------------ land. 

Caucasus foredeep ------- U.S.S.R., Caspian Sea _ 

Large open intermontane Lake Maracaibo ------ basin. 

Subtype B, intermediate be- Malaysia, Brunei; New tween extracontinental Zealand. and intermontane. 

Total -----··------------·------------------------

Extracontinental: 

Subtype A, Hinge belt and trough and fold basin. 

Subtype B, Cratonic margin 

downwarp and embayment. 

Subtype C, Major deltaic deposits in cratonic mar- gin downwarp. 

Subtype D, Major deltaic deposits in subsiding 

trough along margin of small ocean basin. 

Subtype E, Cratonic down- warp and embayment with buried basement highs. 

Total 

Persian Gulf ---------

Congo (Brazzaville) --

Angola-Cabinda ------

Gabon ----·-----------

Northwest Australia __ 

Nigeria --------------

U.S., Gulf of Mexico _ 

Mexico, Gulf of Mexico. 

1 Includes 5 sandstone and 1 limestone reservoirs. 

2 (13) 

9 

1 (6) 1 

15(19) 1 

22 NA 

1 (1) 

(12) 

(6) 1(14) 

2(31) (1) 

4(281) (202) 

2(13) ------

32 (344) 1 (217) 

The Persian Gulf area predominates in this 

third group. Indeed the great magnitude of 

petroleum in the Persian Gulf makes it unique 

among the world's offshore oil fields. The areas 

of major deltaic deposits within the extracontinental basin such as those of the Mississippi 

and Niger Rivers, are typified both by a large 

number of fields and relatively large amounts 

of gas. 

Evaporites are involved as an entrapment 

factor in a large number of geographic areas 

in both intracratonic and extracontinental 

basins. Because of their worldwide importance 

as a factor in petroleum-producing areas, the 

general distribution of known evaporite de23 

2,500- Miocene-- Ss. No 22.1- 1.44-

5,850 Pliocene. 22.6 1.57 600- Pliocene Ss. No NA NA 16,608 

2,200- Miocene-- Ss. No 14.7- 1.47- 11,000 Cretaceous. 27.0 2.68 7,068- Tertiary Ss. No NA NA 10,000 

4,000- Cretaceous- Ls. Yes 35.4 2.30 11,050 Jurassic 

1,900 Tertiary- Ss. Ye!l NA NA U. Cretaceous. 1,350-· Miocene-- Ss. Yes NA NA 8,600 Cretaceous. 4,265- Cretaceous Ss. Yes Wide Wide 

9,384 range. range. 2,200- Jurassic NA No 37.2 0.02 14,000 

4,500- Miocene Ss. No 39.4 0.09 12,000 

2,472- Quaternary- Ss. Yes 20.2- 0.33-

16,900 Miocene. 34.4 0.66 

9,040- Jurassic Ls. No NA NA 11,362 

posits in offshore areas around the world is 

shown on figure 10. 

CONCLUSIONS 

Review of the first quarter century of offshore development permits six salient conclusions: 

1. At the end of the quarter-century that began in 1947, five offshore areas overshadow all others in the amount of petroleum discovered: The Persian Gulf, Lake 

Maracaibo, the northern Gulf of Mexico, 

the North Sea, and offshore southern California. Four of the areas share common 

characteristics : they are ( 1) either close 
1:>:) 

~ 

0 

60 

,, 

''-

' ; I 'I 

' I I 

( I I 

\.._... I \_\ 

' / ' -,' 

2,500-m isobath // 

proximate base of continental slop~ -/ 

<" ' C::> '' 

,....- --,....._ ..... -..-.I 

/~-

/ 

\ 

I 

\ ~0 l) \ 

\ 

,~ 

\ 

f]D 

0 

...., ( ::, ... , 'J \ -) 

\I 

Jl 

c 

_ __. I 

o~ c 

',-;::::;- / I V 1 

'-) 

\ 

l 

\ 

-_; 

''\ I' ,, ,\J, 

~ /(J I I J 

( I \ 

~/ 

FIGURE 10.-Distribution of known major evaporite deposits offshore (shaded). Dots represent areas of salt diapirs. Adapted from McKelvey and 

Wang (1970) . 
to onland areas that were either already 

established as large petroleum producers 

or were known to have a large petroleum 

potential prior to 1947, or (2) extensions 

of large onshore fields. 

Lake Maracaibo had large production 

before 1947, and its petroleum is not considered by some as proper for inclusion 

in offshore statistics, as its offshore fields 

are simply extensions of onshore fields 

beneath shallow lake waters. There is 

some validity to this contention. Consequently, of the five offshore areas having 

the largest reserves, only the central part 

of the North Sea basin is a newly dis., 

covered petroleum province. 

Furthermore, Persian Gulf reserves 

are so large relative to all other areas, 

and the geology of the offshore producing 

fields there is so similar to the geology of 

the onland fields, that it must be classed 

as unique among the offshore producing 

areas. The likelihood of finding another 

Persian Gulf situation elsewhere in the 

offshore seems remote at this time, although recent discoveries in the North 

Sea have been spectacular. Nevertheless, 

none of the giants found there so far 

approaches Safaniya in estimated recoverable reserves. 

If ·the oil discovered in the Persian 

Gulf and Lake Maracaibo are subtracted 

from the total of 172.8 billion barrels of 

estimated recoverable reserves listed in 

table 4, 50 billion barrels remain as the 

fruits of search to date for all other offshore areas-a respectable but not spectacular total considering the effort and 

capital expended. 

2. As has been the situation for onland exploration for the past half-dozen years 

or more, the rate of finding new reserves 

offshore in areas apart from onshore 

producing areas is not keeping pace with 

the rate of increase of consumption of 

petroleum and petroleum products around 

the world. 

For example, it is estimated that by 

1985, when oil fields already discovered 

in the North Sea are expected to reach 

25 

full production capacity, the yearly supply available at that time from fully developed North Sea fields will meet only 

one-sixteenth of northwest Europe's projected yearly demand. Cast in the perspective of reserves versus production, 

the remaining oil reserves offshore at the 

present time, including Lake Maracaibo 

reserves, are approximately as much as 

the world total cumulative production of 

about 282 billion barrels through 1972. 

Hubbert (1971) related cumulative 

worldwide oil production to periods of 

time. He stated (p. 63) that during the 

80-year period from 1890 through 1970 

the average rate of production increase 

has been 6.94 percent per year, with a 

doubling period of 10 years. The 102 

years from 1857 to 1959 were required to 

produce the first half of the cumulative 

production; only the 10-year period from 

1959 to 1969 was required for the second 

half. Within this frame of reference, remaining offshore oil reserves today are 

approximately 95 percent as much as 

worldyvide production over the past 13 

years. World consumption of oil in 1972 

was about 20 billion barrels. Estimated 

consumption for 1975 is 23.8 billion barrels and for 1980, 31.3 billion barrels 

(McCaslin, 1973b, p. 5). Thus, in 1973, 

estimated remaining reserves of oil offshore would supply the world at the current rate of consumpti'on for 6.4 years. 

United States estimated remaining offshore reserves are sufficient to supply 

domestic demands for 1.6 years at the 

1973 rate of consumption. 

3. The rate of discovery worldwide must be 

increased substantially if the offshore is 

to provide a substantial new supply of 

petroleum. During the past 25 years the 

rate of discovery of petroleum offshore 

has averaged about 7 billion barrels per 

year. However, most of the effort has 

come since 1957, and over the past 16 

years the discovery rate has averaged 

closer to 10 billion barrels per year. Statistics on the number of barrels of oil 

discovered offshore relative to footage 
drilled are not available. As already 

pointed out, the geology of much of the 

world's submerged continental margins 

remains relatively unknown. Therefore, 

the offshore search for petroleum must 

be classed as still in an early stage. Furthermore, the importance of giant petroleum fields in supplying most of the 

world's petroleum has been stressed. 

The chronological profile of finding 

giant fields shown in figure 6 must be at 

least maintained if the reserves base is to 

keep pace with the rate of rise in consumption. A substantially increased effort of geologic research and exploration is needed, particularly over the outer 

parts of the margin-the slope and rise 

-which may contain the thicker parts 

of sedimentary basins whose thinner 

parts lie under the continental shelves. 

Intensified research and exploration on a 

worldwide scale is needed if we are to 

develop a more sophisticated understanding of the geology and tectonic processes 

that have molded the continental margins 

over the eons of geologic time. Such an 

effort can greatly increase our ability to 

select more efficiently, more accurately, 

and more quickly those areas of the offshore that have the best potential for 

resources, petroleum as well as hard minerals. The time to make this effort is now 

because the need for new supplies of 

energy obviously is urgent. 

4. Efforts in the United States to examine in 

detail the geologic framework of the submerged continental margins and to appraise the petroleum resource potential 

therein have been far short of both the 

need and the potential. Somewhat less 

than 5 percent of the United States Continental Shelves has been studied in the 

detail necessary to make meaningful estimates of petroleum potential, not to mention that little or no serious investigation 

of the continental slope and rise has been 

made. Yet our submerged continental 

margins in total area are among the 

world's more extensive. 

5. The current trend of exploration for offshore petroleum is into the deeper waters 

26 

of the outer edge of the continental 

shelves and beyond. This trend will inevitably mean increased development 

costs. However, this will be offset, to a 

degree difficult to determine at this time, 

by the use of subsea completion and production units. Development of subsea systems is now in an advanced stage of testing, and, it can be predicted with a fair 

degree of certainty that by the end of 

the next decade most offshore wells will 

be produced from underwater systems. 

Production operations on a large scale 

in water depths exceeding 600 feet (182 

m) will almost certainly require subsea 

systems. Sea-surface platforms simply 

will be too costly and risky for producing 

in deep water. A resume of the current 

status of underwater hardware for subsea production is given by McCaslin 

(1973b, p. 216-223). Advances and trends 

in offshore petroleum technology have 

been summarized by Wang (1971). 

6. Geographic predictions based on geologic 

information about where new offshore 

petroleum provinces might lie are difficult 

to make at this time because knowledge 

is still limited. Some general corollaries 

can be drawn from the geologic resume 

of fields shown in table 7. The largest reserves have been found in the small ocean 

basins, in areas of extensive evaporite 

deposition, in thick sequences of deltaic 

sediments, and in drowned intermontane 

basins. The extensive stretches of continental shelves such as those around 

much of Africa and South America have 

failed to yield large quantities of petroleum. However, these areas fall largely 

within those parts of the offshore where 

geologic conditions are not as yet well 

known. 

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*u.s. GOVERNMENT PRINTING OFFICE: 1974-543-584/1 0 9