OCS Study

BOEM 2020-51

US Department of the Interior

Bureau of Ocean Energy Management

Alaska Region

Oil Spill Occurrence Rates for Cook 

Inlet, Alaska Oil and Gas Exploration, 

Development, and Production 
OCS Study

BOEM 2020-051

US Department of the Interior

Bureau of Ocean Energy Management

Alaska Region

Oil Spill Occurrence Rates for Cook 

Inlet, Alaska Oil and Gas Exploration, 

Development, and Production

October / 2020

Authors:

Tim Robertson, Nuka Research and Planning Group, Lead Author

Lynetta K. Campbell, Statistical Consulting Services, Lead Analyst

Sierra Fletcher, Nuka Research and Planning Group, Editor

Prepared under contract #140M0119F0003

by

Nuka Research and Planning Group, LLC

P.O. Box 175 Seldovia, AK 99663

10 Samoset Street Plymouth, Massachusetts 02360
i

DISCLAIMER

Study concept, oversight, and funding were provided by the US Department of the Interior, Bureau of 

Ocean Energy Management (BOEM), Environmental Studies Program, Washington, DC, under Contract 

Number 140M0119F0003. This report has been technically reviewed by BOEM, and it has been approved 

for publication. The views and conclusions contained in this document are those of the authors and should 

not be interpreted as representing the opinions or policies of the US Government, nor does mention of 

trade names or commercial products constitute endorsement or recommendation for use.

REPORT AVAILABILITY

To download a PDF file of this report, go to the US Department of the Interior, Bureau of Ocean Energy 

Management Data and Information Systems webpage (http://www.boem.gov/Environmental-StudiesEnvData/), click on the link for the Environmental Studies Program Information System (ESPIS), and 

search on 2020-051. The report is also available at the National Technical Reports Library at 

https://ntrl.ntis.gov/NTRL/.

CITATION

Robertson, T., Campbell, L.K. 2020. Oil Spill Occurrence Rates for Cook Inlet, Alaska Oil and Gas 

Exploration, Development, and Production. Anchorage (AK): US Department of the Interior, Bureau 

of Ocean Energy Management. OCS Study BOEM 2020-051. 78 p.

ABOUT THE COVER

Platform A in sea ice in Central Cook Inlet, photo by Tim Robertson.

ACKNOWLEDGMENTS

This project was funded by the Bureau of Ocean and Energy Management (BOEM) contract 

#140M0119F0003 Alaska Oil Spill Occurrence Estimators Study. We thank Dr. Heather Crowley and 

Caryn Smith on the BOEM staff for their review and guidance.
ii

EXECUTIVE SUMMARY

Under contract to the Bureau of Ocean Energy Management (BOEM), Nuka Research and Planning 

Group, LLC developed statistical methods to estimate oil spill occurrence based on past onshore and 

offshore spills in the Cook Inlet region. This information was sought for use in future assessment of 

potential oil and gas leasing, exploration or production in the Outer Continental Shelf managed by 

BOEM, though the current oil and gas production infrastructure is all based onshore or in state waters.

A dataset of 292 spills was compiled from a several sources of available records covering 1966–2019. 

Spills were included in the dataset if they were larger than one barrel and could be associated with Cook 

Inlet oil and gas exploration, development, or production infrastructure or activities. While this included 

oil field support, it did not include the distribution of natural gas or refining and distribution of refined oil

products, nor the shipment of crude oil into Cook Inlet. Spills, as recorded in the data, were consolidated 

into four types: crude oil, diesel, other refined products, and natural gas liquids.

The full dataset was characterized across oil fields and infrastructure types, as well as presenting the 

number and volume of spills over time:

• The oil fields with highest numbers of spills are the legacy fields that have been operating the 

longest: Trading Bay (65), Swanson River (47), and Middle Ground Shoal (37). Likewise, the 

infrastructure components with the largest number of spills have been operating in Cook Inlet for 

more than 50 years: Kenai Pipeline (23) and Cook Inlet Pipeline (13). 

• The largest number (189) and 79% of the volume (12,421 barrels [bbl]) of recorded spills were 

attributed to crude oil. The refined oil category accounted for the next highest number (103) and 

21% of volume (3,205 bbl).

• The largest number (146) and largest volume (11,485 bbl) of recorded spills were attributed to 

mechanical failure. Spills caused by human error (66) represented about 45% of the number of 

spills due to mechanical failure and about 17% of the volume. The cause was unknown for 64 

spills, representing 1,502 bbl.

• The largest number (214) and 65% of the volume (10,163 bbl) of recorded spills were attributed 

to oil production facilities. The crude oil terminal category accounted for the next highest number 

(29) and 24% of volume (3,726 bbl). 

• Most spills (213) were between 1–10 bbl, totaling a volume of 765 bbl. Only 4 spills exceeded 

1,000 bbl each, but these totaled 7,100 bbl by comparison. Seventy-five (75) spills were in the 

range of 10–1,000 bbl totaling 7,770 bbl.

While the full dataset was characterized, only spills from 1996–2019 were used to evaluate trends and 

develop the occurrence estimators. Gaps in earlier data strongly suggested inconsistencies in the dataset, 

and familiarity with the context indicated both that industry practices have changed with time (and 

regulation) and the current and best available data tracking system for the area was initiated in mid-1995. 

The 1996–2019 dataset also predicted spills from 2009–2019 slightly better than a second potential 

variation with data from 1988–2019. Although the latter dataset was larger it did not yield better results.

When comparing spills from 1996–2019 to oil production volumes, the total number of spills of all oil 

types correlates fairly well with production as both generally decline until 2018. That year there is a sharp 

increase in production but no increase in spills. However, annual spill volume does not correlate with 

production well at all. Additionally, when broken down by oil type, it is actually the number of crude oil 

spills that correlates best with production. While both crude and refined spills vary considerably, the trend 

in crude oil spills more closely follows the trend in oil production. There is no readily discernable trend in 

the number of refined product spills. 
iii

Several approaches were tested to develop occurrence estimators. The dependent variables were the total 

volume of oil spilled each year and the total number of spills each year. The candidates for inclusion as 

independent spills were: the annual volume of gas produced from gas wells, the annual volume of crude 

oil produced from oil wells, the annual volume of water produced from oil wells, the average inflation 

adjusted price of Alaskan crude each year, and the length of pipelines transporting oil in the region each 

year. All independent variables, except gas production, resulted in Pearson Correlation Coefficient values 

significant at the 90% confidence level. Overall, the linear correlations were significantly stronger 

between the potential independent variables and the number of spills observed than between the volume 

of oil spilled. This further reinforced the decision to focus the regression work on explaining the number 

of spills, not the volume spilled.

A suitable regression model was identified for the number of spills using oil production as a single 

independent variable:

N_tot = 2.1557 + Oil_Prod. x 0.3591

Where: N_tot = total annual number of spills for all spill types and classes

Oil_ Prod. = annual volume of crude oil produced1 from oil wells in million bbl

The model indicated that for every increase of one million barrels (MMbbl) of crude oil production, the 

number of annual spills is expected to increase 0.36 units (number of spills) for all spill types and classes. 

This model explains 23% of the variation observed in the annual number of spills. The model’s calculated 

multivariate power was 0.7199. The power is adequate but not exceptional. This is attributed to the 

relatively small sample size.

The model’s chief weakness stems from an extreme outlier in the data: in 2019, at an annual oil 

production volume of 5.2 MMbbl, there were 11 spills recorded. The model also was unable to predict 

spills larger than 1,000 bbl since there were no such spills in the 1996-2019 dataset used. A Poisson 

distribution was used to estimate the probability of the expected number of large spills for various total 

production volumes based on all historic Cook Inlet region data.

By contrast, it was not possible to develop a regression model to estimate the annual volume of oil spills. 

Instead, a bootstrapping procedure and Monte Carlo simulation was used to estimate the spill volume.

These estimates were then combined in the following formula to estimate the total annual volume 

expected to be spilled at a given level of oil production:

Vol_toty = Pred_N_toty x Prop_B x Med_B + Pred_N_toty x Prop_C x Med_C + Pred_N_toty x 

Prop_D x Med_D

Where: Pred_N_toty = total number of spills predicted for oil production Y using the regression 

model with multiple realizations created via a Monte Carol simulation

Prop_X = Proportion of spills from Class X estimated using the bootstrapped procedure

Med_X=Median spill size of Class X estimated using the bootstrapped procedure

This method resulted in an estimated 87 bbl of annual oil spill volume with a 95% confidence interval of 

6 to 226 bbl at an annual level of 7.5 MMbbl of oil production.

 

1 Does not include natural gas liquids.
iv

Occurrence estimates were also sought for crude and refined spills separately. The occurrence model to 

predict annual number of crude oil spills is very similar to the model developed to predict annual number 

of all types of oil. Applying the above modeling approach to the Cook Inlet annual crude oil spill data 

resulted in a regression model with Oil Production as the single independent variable.

The resulting linear regression model was: 

N_crude_tot = -0.1432 + Oil Prod. x 0.3209

Where: N_crude_tot = total annual number of crude oil spills

Oil_ Prod. = annual volume of crude oil produced2 from oil wells in million bbl 

The model indicates that for every increase of one million bbl of oil production the number of annual 

crude oil spills is expected to increase 0.32 units. The model explains 25.58% of the variation observed in 

the annual number of spills. 

The model was not useful for predicting annual numbers of refined spills, however. There was no 

significant relationship between annual number of refined oil spills and any of the independent variables 

investigated. The best estimator of the annual number of refined oil spills is the mean value, which is 

equal to 2.6 refined oil spills per year. 

The limitations of the models developed should be noted. These include the small size of the dataset and 

changes in reporting over time. Occurrence estimates might also be improved by using more independent 

variables, though in order to be useful these need to be variables that can be estimated or planned on for 

the future. 

 

2 Does not include natural gas liquids.
v

Contents

1 INTRODUCTION ...........................................................................................................................10

1.1 Purpose ................................................................................................................................10

1.2 Project Scope .......................................................................................................................10

1.2.1 Cook Inlet Oil and Gas Operations....................................................................................10

1.2.2 Spill Source ......................................................................................................................14

2 METHODS AND ASSUMPTIONS..................................................................................................15

2.1 Oil Spill Data Collection and Collation....................................................................................15

2.1.1 Spill Size Classes .............................................................................................................16

2.1.2 Spill Substance.................................................................................................................17

2.1.3 Activity/Facility ..................................................................................................................17

2.1.4 Spill Source ......................................................................................................................18

2.1.5 Spill Cause .......................................................................................................................18

2.1.6 Spill Records and Years Included in Final Dataset ............................................................19

2.2 Exposure Variable Data ........................................................................................................19

3 SUMMARY OF HISTORICAL SPILL OCCURRENCE DATA..........................................................19

3.1 Total Spills Over Time...........................................................................................................19

3.2 Overview of Recorded Spills .................................................................................................19

3.2.1 Spill Occurrence by Oil Field or Infrastructure Component.................................................20

3.2.2 Overall Spill Occurrence by Cause....................................................................................22

3.2.3 Spill Occurrence by Activity/Facility Type ..........................................................................23

3.2.4 Spill Occurrence by Substance Type.................................................................................24

3.2.5 Summary Spill Data by Size Class ....................................................................................25

4 TREND ANALYSIS........................................................................................................................27

4.1 Choosing a Timeframe for Trend and Occurrence Analysis ...................................................27

4.2 Annual Data vs. Monthly Data...............................................................................................28

4.3 Seasonal Variation in Cook Inlet Spill Rates ..........................................................................29

4.4 Spill Trends by Year..............................................................................................................30

4.5 Spill Trends by Product Type ................................................................................................31

5 SPILL RATE OCCURRENCE ESTIMATES....................................................................................33

5.1 Annual Number of Spills Over Time.......................................................................................33

5.1.1 Screening Independent Variables......................................................................................33
vi

5.1.2 Modeling Approach...........................................................................................................35

5.2 Predicting Annual Spill Numbers from Crude Oil Production Using Linear Regression ..........35

5.2.1 Predicting Large Spills ......................................................................................................38

5.3 Predicting Annual Spill Volume from Crude Oil Production ....................................................39

5.4 Estimating Occurrence Rates by Oil Type .............................................................................43

5.4.1 Occurrence Rates for Number of Spills by Oil Type...........................................................43

5.4.2 Occurrence Rates for Annual Volume of Spills by Oil Type................................................45

6 CONCLUSIONS ............................................................................................................................46

6.1 Limitations and Challenges of Occurrence Models ................................................................46

6.2 Occurrence Estimates for Spill Number.................................................................................46

6.3 Occurrence Estimates for Spill Volume..................................................................................46

6.4 Recommendations ................................................................................................................47

7 REFERENCES ..............................................................................................................................47

8 APPENDICES................................................................................................................................50

Appendix A: Collated Oil Spill Dataset....................................................................................................51

Appendix B: Exposure Variable Datasets...............................................................................................75
vii

List of Figures

Figure 1. Cook Inlet oil and gas units .....................................................................................................12

Figure 2. Cook Inlet oil and gas production infrastructure and related units.............................................13

Figure 3. Cook Inlet process flow diagram..............................................................................................14

Figure 4. Spill number and volume by cause, activity/facility, substance and oil field/infrastructure in Cook 

Inlet, 1966–2019....................................................................................................................................20

Figure 5. Overview of Cook Inlet spills by size class, cause, activity, substance, and oil field, 1966–2019

..............................................................................................................................................................25

Figure 6. Number of recorded oil spills by size class in Cook Inlet, 1966–2019.......................................27

Figure 7. Comparison of the frequency distribution for spills per month vs. spills per year for Cook Inlet 

spills, 1996–2019...................................................................................................................................29

Figure 8. Total number of oil spills by month in Cook Inlet, 1996–2019...................................................29

Figure 9. Annual recorded number of oil spills plotted against the annual crude oil production for Cook 

Inlet, 1996–2019....................................................................................................................................30

Figure 10. Annual recorded volume of oil spills plotted against the annual oil production for Cook Inlet, 

1996–2019 ............................................................................................................................................31

Figure 11. Annual recorded number of oil spills for crude oil and refined oil plotted against the annual oil 

production for Cook Inlet, 1996–2019.....................................................................................................32

Figure 12. Annual recorded volume of oil spills for crude oil and refined oil plotted against the annual oil 

production for Cook Inlet, 1996–2019.....................................................................................................32

Figure 13. Scatterplot matrix, distribution, and the Pearson Correlation Coefficient for each variable 

considered for inclusion in the Cook Inlet modeling process...................................................................34

Figure 14. Predicted value, 95% confidence interval, and 95% prediction interval for the expected number 

of all Cook Inlet oil spills for the range of oil production values studied ...................................................37

Figure 15. Distribution of volume of recorded oil spill in Cook Inlet, 1996–2019 ......................................39

Figure 16. Bootstrap estimate of the distribution of proportions for each spill class .................................41

Figure 17. Bootstrap/Monte Carlo estimate of the predicted annual volume of Cook Inlet oil spilled vs 

annual crude oil production ....................................................................................................................43

Figure 18. Predicted value, 95% confidence interval, and 95% prediction interval for the expected number 

of crude oil spills for the range of annual oil production values studied ...................................................44
viii

List of Tables

Table 1. Variables for each spill record ..................................................................................................16

Table 2. Year of first production from Cook Inlet productions units..........................................................21

Table 3. Cook Inlet area spills by oil field/infrastructure category, 1966–2019.........................................21

Table 4. Largest recorded spill at each Cook Inlet oil field and percent of total volume of spills from that 

field represented by the largest spill, 1966–2019....................................................................................22

Table 5. Cook Inlet spill occurrence and percent of total spill volume by cause, 1966–2019....................23

Table 6. Cook Inlet spill occurrence and percent of total spill volume by facility type, 1966–2019............24

Table 7. Cook Inlet spill occurrence and percent of total spill volume by substance, 1966–2019.............24

Table 8. Cook Inlet spill occurrence and percent of total spill volume by size class, 1966–2019..............26

Table 9. Class A and Class B spills........................................................................................................26

Table 10. Pearson Correlation Coefficient and p-value for independent variables related to annual number 

and volume of spills recorded in Cook Inlet, 1996–2019.........................................................................35

Table 11. Statistics for the linear regression model predicting annual spills number from oil production ..36

Table 12. Expected number of large spills over the total production volume of a Cook Inlet Oil...............38

Table 13. Pearson Correlation Coefficient and p-value for independent variables related to annual volume 

of spills recorded in Cook Inlet, 1996–2019............................................................................................39

Table 14. Expected annual number of Cook Inlet spills for all size classes and corresponding 95% 

confidence interval for five levels of oil production..................................................................................42

Table 15. Median Cook Inlet spill size by class and corresponding 95% confidence interval for Cook Inlet 

recorded spill 1996–2019.......................................................................................................................42

Table 16. Expected annual number of Cook Inlet spills and corresponding 95% confidence interval four 

size classes and five levels of oil production; and estimated total annual volume of spills predicted from 

the bootstrap/Monte Carlo model ...........................................................................................................42

Table 17. Statistics for the linear regression model predicting annual number of crude oil spills from oil 

production .............................................................................................................................................44

Table 18. Median annual spill volume and 95% percentile interval by oil type for Cook Inlet spills 1996–

2019......................................................................................................................................................45

Table B-1. Cook Inlet in-scope pipeline miles, 1960-2019.......................................................................75

Table B-2. Adjusted Alaska North Slope crude oil pricing, 1996-2019.....................................................76

Table B-3. Cook Inlet gas production per year, 1958-2019 .....................................................................77

Table B-4. Cook Inlet oil production per year, 1958-2019 .......................................................................78
ix

List of Abbreviations and Acronyms

ADEC Alaska Department of Environmental Conservation

AIC statistic Akaike Information Criteria

Bbbl Billion barrels

bbl barrel

BOEM Bureau of Ocean Energy Management

CIGGS Cook Inlet Gas Gathering System

DOI US Department of the Interior

mcf million cubic feet 

MMbbl Million barrels

NGL Natural Gas Liquids

NRC National Response Center

OCS Outer Continental Shelf

RMSE root mean square error

VIF statistic Variable Inflation Factor
10

1 INTRODUCTION

Nuka Research and Planning Group, LLC completed this study under Contract #140M0119F0003 to the 

Bureau of Ocean Energy Management (BOEM) Alaska Regional Office.

1.1 Purpose

The purpose of project was to develop oil spill occurrence estimators for the Cook Inlet region in Alaska

based on available data on past onshore and offshore spills in the region. 

The objectives of this analysis were to: 

• Develop a dataset of crude and refined oil spill records for Cook Inlet, Alaska;

• Develop a dataset of crude oil and gas production, pipeline mileage, and other possible 

independent variables for developing an oil spill occurrence rate model for Cook Inlet, Alaska;

• Provide statistical measures of crude and refined oil spills such as mean and median spill sizes 

with confidence intervals as appropriate;

• Use statistical analysis to identify trends in spill numbers and volumes;

• Categorize Cook Inlet spills into size classes;

• Apply statistical procedures to develop occurrence rate estimator models for crude and refined oil 

spills, as well as all spills; and

• Develop an appropriate confidence interval for occurrence rate estimators.

Previous studies have provided methodologies for estimating oil spill occurrence rates for both offshore 

and onshore oil and gas development. However, most of the previous work on Outer Continental Shelf 

(OCS) historical platform and pipeline crude oil spill occurrence rates relies on data from the Gulf of 

Mexico and Pacific OCS (ABS Consulting Inc. 2016; ABSG Consulting Inc. 2018; Anderson and 

LaBelle, 2000; Eschenbach et al., 2010; Anderson et al., 2012). The BOEM Alaska Regional Office

contracted this analysis to calculate onshore and offshore spill occurrence based on data collated from 

Alaska's Cook Inlet region, and to include all spills greater than one barrel. 

This report represents the first attempt to estimate oil spill occurrence based on historic spills from Cook 

Inlet oil and gas operations, though estimates of the probability and movement of large spills in the Cook 

Inlet OCS have been generated based on spill occurrence data from other locations (Anderson et al., 2012,

ABS Consulting Inc. 2016; Ji et al., 2016). Previous studies using Alaska-specific oil spill data have 

focused on Alaska's North Slope (Hart Crowser, 2000; Nuka Research, 2010; Robertson et. al., 2013).

1.2 Project Scope

For the purpose of the study, the project scope was defined by the geographic area and whether the spill 

was associated with oil and gas exploration or production activities.

1.2.1 Cook Inlet Oil and Gas Operations

Crude oil was first found in the Cook Inlet area in the 1950s, at the Swanson River field (Eastham, 2014). 

Today, oil and gas are produced both onshore and offshore in multiple units extending as far south as 

Anchor Point, Alaska (see Figure 1). To date, all of the offshore production has been in State waters and
11

oil production infrastructure is concentrated in Central Cook Inlet (see Figure 2). This infrastructure

includes 17 fixed offshore oil production platforms and one terminal loading platform, various production 

facilities, a refinery, hundreds of miles of pipelines, storage facilities, and marine terminals (one in 

Nikiski and a second, now inactive, at the Christy Lee Platform at the Drift River Terminal). Pipelines 

within the project scope transport three-phase liquids (a mix of oil, gas, and water before processing 

occurs), crude oil, produced water, and, in a few cases, fuel gas that is delivered to platforms.

The Marathon refinery in Nikiski processes crude oil from Cook Inlet as well as oil brought by vessel 

from other areas (notably the Trans-Alaska Pipeline System terminus in Prince William Sound). Crude oil 

may be shipped out of Cook Inlet from Nikiski as well, although it has not been done in many years. Prior 

to 2018, crude oil was also shipped within Cook Inlet from the Drift River Terminal/Christy Lee Platform 

to the Kenai Pipeline dock on the east side (or shipped out of the Inlet). Currently, oil produced from the 

platforms connected to the west side infrastructure is moved to the east side via a repurposed subsea gas 

pipeline (Boettger, 2018).

In addition to the infrastructure shown in Figure 2, there are natural gas lines and a refined product 

pipeline to Anchorage. These facilities are outside the scope of this report.
12

Figure 1. Cook Inlet oil and gas units

The Cook Inlet area has both onshore and offshore production of oil and gas.
13

Figure 2. Cook Inlet oil and gas production infrastructure and related units

Oil production in Cook Inlet occurs both onshore and offshore. The East Forelands Production Facility represents the 

point where subsea pipelines come on shore on the East side as well as the Middle Ground Shoal production facility, 

Cook Inlet Gas Gathering System (CIGGS), and Furie gas production facility. There are two marine terminals: one at 

Drift River that is no longer in use but was active for most of the years included in the dataset, and one that remains 

active at the Kenai Pipeline Dock. In total there are 17 fixed offshore production platforms in Cook Inlet. The Christy 

Lee platform depicted was used for loading only. Mobile drilling units have been used in the recent past as well.
14

1.2.2 Spill Source

The study focused on spills associated with oil and gas exploration and production activities. This 

includes much, but not all, of the oil and gas infrastructure in Cook Inlet. Figure 3 shows the basic 

process flow and what elements are in or out of the scope of this study. Spills were included in the data 

analyzed if they were associated with exploration and development activities, production (onshore or 

offshore), or the transport or processing of crude oil up to the point of either being refined in Nikiski or 

shipped out of Cook Inlet. Most of the transport among the included elements occurs via pipeline. Spills 

included in the data did not need to come directly from this infrastructure (e.g., a pipeline leak), but 

simply had to be associated with it. Thus, a diesel spill from a vessel servicing a platform would be 

included.

As shown in Figure 3, spills were excluded if they were downstream of the refinery (either in a tank 

vessel or pipeline), or related to the distribution of natural gas. Spills associated with the shipment of 

crude oil into Cook Inlet also were excluded. For example, the spill associated with the grounding of the 

T/V Glacier Bay in 1987 was excluded because it was carrying Alaska North Slope crude oil to the 

refinery at Nikiski and thus was not associated with oil and gas exploration or production in Cook Inlet.

Figure 3. Cook Inlet process flow diagram
15

2 METHODS AND ASSUMPTIONS

This section describes the methods, inputs, and assumptions applied to the analysis.

2.1 Oil Spill Data Collection and Collation

Nuka Research collated data from various sources including:

• Alaska Department of Environmental Conservation (ADEC) oil spill database

• Reports of oil spills to federal agencies through the National Response Center (NRC)

• Pipeline and Hazardous Materials Safety Administration database report from September 11, 

2018, provided by BOEM

• Epstein, 2002

• Roberts, 1996 

• Robertson, et. al., 2013

• Sienkiewicz, et. al., 1992 

• Whitney, 2002.

Each spill record was reviewed. Spills of larger than 1 bbl were included in the data if they were deemed 

to originate from infrastructure or activities within the project scope. Spills were then categorized based 

on the information available and the best professional judgement of the Principle Investigator. Ten 

percent of records were randomly selected and verified back to the original source.

The original oil spill datasets also each had different data structures. The collation process involved 

transforming each dataset into a common format that would facilitate the merging of records from a single 

spill. In all cases, spill volumes were converted to barrels. In some datasets, multiple variables from a 

single record were concatenated into a single variable. Table 1 presents the data scheme for the final 

dataset with notes about how these variables relate to the original datasets. The final dataset (Appendix A) 

consists of 292 records with each representing a single spill event covering calendar years 1966 through 

2019.
16

Table 1. Variables for each spill record

Variable Information

Spill ID Unique identifier for this dataset. Cook Inlet spill beginning with “CI –"

Primary Source The primary source record for the spill. 

Source ID The identifier from the primary source.

Additional Sources Other sources where a record of the spill was found.

Spill Date The date that the spill occurred, if it was known.

Spill Year The calendar year that the spill occurred.

Spill Size (bbl) The best or maximum estimate of the spill size in barrels (42 US 

gallons). In most instances, tables in this report round to the nearest 

barrel, but fractions of a barrel are preserved in the dataset and used 

in calculations.

Spill Size Class Spill size category. See Section 2.1.1.

Substance The category of the oil substance spilled. See Section 2.1.2.

Consolidated 

Substance

A consolidation of oil substances. See Section 2.1.2.

Facility/Activity Type The category of facility type. See Section 2.1.3.

Consolidated 

Facility/Activity Type

A consolidation of facility types. See Section 2.1.3.

Location The category of the location of the spill, either Offshore, Onshore, or 

Unknown.

Oil Field/Infrastructure The oil field or infrastructure where the spill occurred. See Section 

3.2.1.

Spill Source The category of the source of the spill. See Section 2.1.4.

Spill Cause The category of the spill cause. See Section 2.1.5.

Consolidated Spill 

Cause

A consolidation of spill causes. See Section 2.1.5.

2.1.1 Spill Size Classes

Only spills larger than one barrel (bbl) were included. The following spill size classes, as defined in 

Robertson et al. 2013, were used for this study:

• A = oil spills > 1,000 bbl

• B = oil spills > 200 bbl and ≤ 1,000 bbl

• C = oil spills > 10 bbl and ≤ 200 bbl

• D = oil spills > 1 bbl and ≤ 10 bbl

• E = oil spills ≤ 1 bbl (excluded from this analysis)

Spills less than or equal to one barrel were not considered because of the historical inconsistency in 

reporting of small spills. 
17

2.1.2 Spill Substance

The following consolidated spill substances were used:

• Crude Oil

• Crude Oil and Produced Water

• Refined: Diesel

• Refined: Natural Gas Liquids

• Refined: Other

Consolidated spill substances were developed based on the categories used:

• Crude Oil

• Crude Oil and Produced Water

• Refined: Asphalt

• Refined: Aviation

• Refined: Ballast Water with Oil

• Refined: Bunker Oil

• Refined: Diesel

• Refined: Gasoline

• Refined: Hydraulic Oil

• Refined: Jet Fuel

• Refined: Lube/Gear Oil

• Refined: Naphtha

• Refined: Natural Gas Liquids

• Refined: Turbine Oil

• Refined: Unknown

• Refined: Unknown and Water

Where spills were of a mixed substance type, such as crude oil and produced water, only the oil portion of 

the mixture was included in the final dataset. For spills of produced water and oil where the proportion of 

oil and water was not identified, the total volume of the mixture was recorded and the proportion was 

estimated during the analysis, given the best information available from the data source.

2.1.3 Activity/Facility 

The following consolidated activity/facility types were used:

• Oil Production

• Oil Exploration

• Support Facility/Services

• Unknown

Consolidated activity/facility types were developed based on the categories used: Crude Oil Terminal (Oil 

Production)

• Natural Gas Production (Oil Production)

• Oil Exploration (Oil Exploration)

• Oil Production (Oil Production)

• Pipeline (Oil Production)

• Support Dock (Support Facility/Services)

• Transmission Pipeline (Oil Production)

• Unknown (Unknown)

• Vehicle (Support Facility/Services)

• Vessel (Support Facility/Services)
18

2.1.4 Spill Source

The following spill source categories were used:

• Coiled Tubing Unit

• Container, Other

• Drill activities

• Drum(s)

• Equipment Failure, Vehicle

• Flare

• Fuel Pump

• Heavy Equipment

• Hydraulic System

• J TUBE

• Loading Arm

• Other

• Pipe or Line

• Tank, Aboveground

• Tank, Mobile

• Tank, Other

• Unknown

• Vehicle

• Vessel

• Vessel Transfer

• Well

2.1.5 Spill Cause

The following consolidated spill causes were used:

• Human Error: Other

• Human Error: Overfill

• Human Error: Unknown

• Mechanical Failure: Corrosion

• Mechanical Failure: Other

• Mechanical Failure: Overpressure

• Mechanical Failure: Unknown

• Mechanical Failure: Valve/Seal

• Other

• Unknown

Consolidated spill causes were developed based on the categories used:

• Cargo Not Secured

• Collision/Allision/Grounding

• Containment Overflow

• Corrosion

• Crack

• Dumping

• Equipment Failure, Gauge/Site Glass 

Failure

• Equipment Failure, Line Failure

• Equipment Failure, Other

• Equipment Failure, Seal Failure

• Equipment Failure, Tank Failure

• Equipment Failure, Unknown

• Equipment Failure, Valve Failure

• Equipment Failure, Vehicle

• Erosion

• External Factors

• Fire/Explosion

• Freezing

• Hull Failure

• Human Error

• Human Error, Overfill

• Miss-injection

• Other

• Over Pressure

• Puncture

• Rollover/Capsize

• Unknown

• Weld Failure
19

2.1.6 Spill Records and Years Included in Final Dataset

The final oil spill dataset from 1966–2019 included 292 spills larger than one barrel. As discussed in 

Section 4 however, a shorter time period was used for the development of the occurrence estimator.

2.2 Exposure Variable Data

Data on crude oil production for all years from 1958 through 2019 by month was compiled from the 

Alaska Oil and Gas Conservation Commission’s records and combined into a workbook with a separate 

spreadsheet for each of the 11 distinct producing Cook Inlet oil fields. Data for each month includes 

barrels of oil produced, barrels of water produced, million cubic feet of gas produced, and number of 

producing wells. Note that natural gas liquids were not included in these data.

Data on pipeline mileage were taken from the Cook Inlet Infrastructure Assessment conducted by Nuka 

Research for ADEC in Fletcher et. al. (2020). Because the price for Cook Inlet crude oil is based on the 

price of Alaska North Slope crude, the adjusted Oil Price data for Alaska North Slope crude oil were

taken from U.S. Energy Information Administration (EIA, 2020) and adjusted for the Consumer Price 

Index3 to 2020 US dollars. 

These data, which are included in Appendix B, were screened as independent variables for developing 

occurrence estimators.

3 SUMMARY OF HISTORICAL SPILL OCCURRENCE DATA 

This section summarizes the spill data from 1966–2019 by the number of spills, spill volume, oil field, 

facility/activity type and cause, examining each of these factors as related to the spill size categories.

3.1 Total Spills Over Time

There were 292 spills recorded in the final dataset for Cook Inlet. The earliest spill in the dataset occurred 

on March 5, 1966 and the last spill occurred on December 27, 2019. The year was recorded for every 

spill, though the month and day were missing from 88 of the spill events recorded prior to 1994. 

3.2 Overview of Recorded Spills

This section summarizes oil spill occurrence for all spills in the dataset from 1966–2019. It presents the 

spill data based on oil field, cause, facility type, and substance spilled, including a breakdown by size 

class. Figure 4 shows the number and volume of recorded spills for each cause, activity, substance, and 

oil field/infrastructure. Each of these factors will be discussed independently in sections below.

 

3 Consumer Price Index for all Urban Consumers (CPI-U) as presented by the Bureau of Labor Statistics
20

Figure 4. Spill number and volume by cause, activity/facility, substance and oil field/infrastructure 

in Cook Inlet, 1966–2019

3.2.1 Spill Occurrence by Oil Field or Infrastructure Component

Oil was first produced in Cook Inlet in 1958 as shown in Table 2. This section presents spill occurrence 

by oil field or infrastructure component, as shown in Table 3. The oil fields with highest numbers of spills 

are the legacy fields that have been operating the longest: Trading Bay (65), Swanson River (47), and 

Middle Ground Shoal (37). Likewise, the infrastructure components with the largest number of spills 

have been operating in Cook Inlet for more than 50 years: Kenai Pipeline (23) and Cook Inlet Pipeline 

(13).

The volume of recorded oil spills is dominated by the Middle Ground Shoal oil field (6,431 bbl) with 

41% of the total volume spilled. Almost 75% of the Middle Ground Shoal total is from the three Class A 

oil spills described below and if the 1,000 bbl Class B spill, which is just below the cut off for Class A, is 

considered, the proportion of Middle Ground Shoal oil spills accounted for by large spills is 90%. Cook 

Inlet Pipeline infrastructure (3,139 bbl) holds the second highest volume with 20% of the total for the 

whole area. Almost 75% of the Cook Inlet Pipeline total is accounted for by the 2,300 bbl spill in 1990. 

The only other infrastructure and oil field components that exceed 1,000 bbl in total volume spilled were 

the Trading Bay oil field (1,301 bbl) and the Kenai Pipeline (1,007 bbl).
21

Table 2. Year of first production from Cook Inlet productions units

Production Unit Year of First 

Production

Swanson River 1958

Kenai 1960

Beluga River 1963

Granite Point 1965

Middle Ground Shoal 1965

Trading Bay 1965

Ninilchik 1966

Redoubt Shoal 1968

North Cook Inlet 1969

Beaver Creek 1972

West McArthur River 1991

Table 3. Cook Inlet area spills by oil field/infrastructure category, 1966–2019

Oil Field - Infrastructure Number Percent 

Number

Total Volume

(bbl)

Percent 

Total 

Volume

Middle Ground Shoal 37 13% 6,430 41%

Cook Inlet Pipeline 13 4% 3,139 20%

Trading Bay 65 22% 1,301 8%

Kenai Pipeline 23 8% 1,007 6%

Granite Point 24 8% 770 5%

Unknown 28 10% 727 5%

Swanson River 47 16% 525 3%

Beaver Creek 1 <1% 500 3%

North Cook Inlet 4 1% 498 3%

Support Services 15 5% 386 2%

Kenai Gas 8 3% 156 1%

Exploration 8 3% 107 1%

West McArthur River 11 4% 55 <1%

Beluga River 3 1% 10 <0.1%

Cosmopolitan 2 1% 7 <0.1%

Redoubt 2 1% 6 <0.1%

Ninilchik 1 <1% 2 <0.1%

Grand Total 292 100% 15,626 100%
22

Table 4 shows the percentage of the total volume spilled accounted for by the largest oil spill in each oil 

field/infrastructure category. Excluding unknowns, the largest oil spill accounted for more than 50% of 

the total volume spilled in eight of the 16 categories. 

Table 4. Largest recorded spill at each Cook Inlet oil field and percent of total volume of spills 

from that field represented by the largest spill, 1966–2019

Oil Field - Infrastructure Maximum Spill 

(bbl)

% Total Volume

Beaver Creek 500 100%

Ninilchik 2.2 100%

North Cook Inlet 490 98%

Kenai Gas 123.8 80%

Redoubt 4.8 79%

Cook Inlet Pipeline 2,300 73%

Cosmopolitan 4 60%

Exploration 60 56%

Granite Point 380 49%

Beluga River 4.8 47%

West McArthur River 25 45%

Kenai Pipeline 400 40%

Swanson River 200 38%

Unknown 261.9 36%

Support Services 126.1 33%

Middle Ground Shoal 2,000 31%

Trading Bay 315 24%

3.2.2 Overall Spill Occurrence by Cause

Table 5 shows the number and volume of oil spills by cause. Half of the spills (146) were due to 

mechanical failure accounting for 74% of the volume. Spills caused by human error (66) represented

about 23% of the number of spills and about 13% of the volume. The cause was unknown for 64 spills, 

representing 1,502 bbl.
23

Table 5. Cook Inlet spill occurrence and percent of total spill volume by cause, 1966–2019

Consolidated Cause Number Percent 

Number

Total Volume

(bbl)

Percent 

Total 

Volume

Mechanical Failure 146 50% 11,485 74%

Mechanical Failure: Other 75 26% 8,229 53%

Mechanical Failure: Valve/Seal 41 14% 2,993 19%

Mechanical Failure: Corrosion 18 6% 211 1%

Mechanical Failure: Unknown 12 4% 52 <1%

Human Error 66 23% 1,989 13%

Human Error: Unknown 34 12% 846 5%

Human Error: Other 11 4% 707 5%

Human Error: Overfill 21 7% 436 3%

Unknown 64 22% 1,502 10%

Other 16 5% 650 4%

Grand Total 292 100% 15,626 100%

3.2.3 Spill Occurrence by Activity/Facility Type

Table 6 shows the number and volume of oil spills by activity/facility type. The largest number (214) and 

65% of the volume (10,163 bbl) of recorded spills were attributed to oil production facilities. The crude 

oil terminal category accounted for the next highest number (29) and 24% of volume (3,726 bbl). All 

other facility categories only accounted for a total of 49 spills and 11% of the volume (737 bbl). It is 

likely that there is overlap and inconsistency in reporting of facility type in these data. For instance, spills 

from pipelines may be recorded under oil production.
24

Table 6. Cook Inlet spill occurrence and percent of total spill volume by facility type, 1966–2019

Activity/Facility Type Number Percent 

Number

Total Volume

(bbl)

Percent 

Total 

Volume

Oil Production 214 73% 10,163 65%

Crude Oil Terminal 29 10% 3,726 24%

Natural Gas Production 16 5% 545 3%

Pipeline 2 1% 420 3%

Vessel 8 3% 358 2%

Transmission Pipeline 4 1% 147 1%

Unknown 6 2% 139 1%

Oil Exploration 8 3% 107 1%

Support Dock 3 1% 19 <1%

Vehicle 2 1% 2 <1%

Grand Total 292 100% 15,626 100%

3.2.4 Spill Occurrence by Substance Type

Table 7 shows the number and volume of oil spills by substance. The largest number (189) and 79% of 

the volume (12,421 bbl) of recorded spills were attributed to crude oil. The refined oil category accounted 

for the next highest number (103) and 21% of volume (3,205 bbl). The relationship between crude oil and 

refined product is likely proportional to the volume of products available to spill. Crude oil is the product 

produced and transported by infrastructure, diesel is a primary fuel to run the process (natural gas is also 

used), and other refined products are used in many other processes, but in relatively small quantities.

Natural gas liquids are a product of processing natural gas and are thus treated as a refined product.

Table 7. Cook Inlet spill occurrence and percent of total spill volume by substance, 1966–2019

Substance Number Percent 

Number

Total Volume

(bbl)

Percent 

Total 

Volume

Crude 189 65% 12,421 79%

Crude Oil 186 64% 12,390 79%

Crude Oil and Produced Water 3 1% 31 0%

Refined 103 35% 3,205 21%

Refined: Diesel 49 17% 2,089 13%

Refined: Other 51 17% 613 4%

Refined: Natural Gas Liquids 3 1% 503 3%

Grand Total 292 100% 15,626 100%
25

3.2.5 Summary Spill Data by Size Class

Figure 5 presents the volume of recorded oil spills by size class for cause, activity/facility type, substance, 

and oil field/infrastructure.

Figure 5. Overview of Cook Inlet spills by size class, cause, activity, substance, and oil field, 

1966–2019

Table 8 shows the number and volume of recorded oil spills by size class. Notice that the relationship 

between number and volume is inverse. The Class A contains the lowest number (4) and the largest 

volume (7,100). The smallest spill size category contains 73% of the number of spills (213), but 

represents only 5% of the total volume spilled (756 bbl).
26

Table 8. Cook Inlet spill occurrence and percent of total spill volume by size class, 1966–2019

Size Class Number Percent Total Volume

(bbl)

Percent Total 

Volume

A > 1,000 bbl 4 1% 7,100 45%

B > 200 bbl & ≤ 1,000 bbl 11 4% 4,529 29%

C > 10 bbl & ≤ 200 bbl 64 22% 3,241 21%

D > 1 bbl & ≤ 10 bbl 213 73% 756 5%

Grand Total 292 100% 15,626 100%

Table 9 presents the four Class A (> 1,000 bbl) and the 11 Class B (>200 and ≤1,000 bbl) oil spills

recorded in Cook Inlet. The largest spill of 2,300 bbl (March 1990) was from a mechanical failure of a 

pipeline at Drift River Terminal which was then operated by Cook Inlet Pipeline. The second largest spill 

of 2,000 bbl (December 1988) was from a mechanical failure of a tank at the Middle Ground Shoal 

production facility in Nikiski operated by Shell Western. The third and fourth largest spills of 1,400 bbl 

each occurred in 1967 and 1968 from subsea pipelines connecting offshore platforms to the Middle 

Ground Shoal production facility operated at the time by Amoco. Both of these spills were likely caused 

by current-induced vibrations causing the pipeline to fail (Belmar, 1993). It should also be noted that 

there was a spill of 1,000 bbl, just below the Class A threshold, in 1968 at Middle Ground Shoal. This 

1968 spill was also used in the calculation of large spill occurrence rate in Section 5.2.1.

Table 9. Class A and Class B spills

Date Spill Volume (bbl) Oil Field Location Source Cause

Class A Spills

12/13/66 1,400 Middle Ground Shoals Offshore Pipe or Line Mechanical Failure: Other

8/11/67 1,400 Middle Ground Shoals Offshore Pipe or Line Mechanical Failure: Other

12/8/88 2,000 Middle Ground Shoals Onshore Tank Mechanical Failure: Other

3/10/90 2,300 Cook Inlet Pipeline Onshore Pipe or Line Mechanical Failure: Valve/Seal

Class B Spills

4/17/68 315 Trading Bay Offshore Pipe or Line Mechanical Failure: Other

6/6/68 380 Granite Point Offshore Pipe or Line Mechanical Failure: Other

10/23/68 1,000 Middle Ground Shoals Offshore Pipe or Line Mechanical Failure: Other

6/10/05 400 Unknown Onshore Unknown Unknown

6/14/05 370 Kenai Pipeline Onshore Pipe or Line Mechanical Failure: Other

1/4/92 214 Kenai Pipeline Onshore Pipe or Line Mechanical Failure: Other

6/15/05 500 Cook Inlet Pipeline Onshore Pipe or Line Other

12/28/93 490 Cook Inlet Pipeline Onshore Unknown Mechanical Failure: Other

3/6/97 378 Trading Bay Offshore Unknown Unknown

11/30/04 220 Beaver Creek Onshore Tank Human Error: Unknown

11/19/16 262 North Cook Inlet Onshore Pipe or Line Unknown
27

4 TREND ANALYSIS

4.1 Choosing a Timeframe for Trend and Occurrence Analysis

Review of the 1966-2019 dataset compiled for this project (and summarized in Section 3) indicated that 

data prior to 1996 appeared less reliable than 1996–2019. While the first production data for Cook Inlet 

occurred in November 1958, the first spill record in the dataset did not occur until more than six years 

later (March 1966). The March 1966 spill was 100 bbl. The first small spill (Class D ≤ 10 bbl) identified 

did not occur until 1967. No spill records were found for some years (1973, 1979–1985; see Figure 6). 

This was believed to be attributed to inconsistent early reporting and databasing procedures. 

Figure 6. Number of recorded oil spills by size class in Cook Inlet, 1966–2019

While the full dataset was characterized, only spills from 1996–2019 were used to evaluate trends and 

develop the occurrence estimators. Gaps in earlier data strongly suggested inconsistencies in the dataset, 

and familiarity with the context indicated both that industry practices have changed with time (and 

regulation) and the current and best available data tracking system for the area was initiated in mid-1995. 

The under-counting of spills prior to 1988 would render any computed mean spill volumes highly 

inaccurate. For this reason, these numbers were not useful in efforts to predict mean volumes or expected 

numbers of spills. 

Two timeframes were considered for a trend analysis: 1988-2019 and 1996-2019. The earlier time frame 

was initially considered desirable because it would offer a larger sample size (31 vs. 23 years) and thus 

more statistical power to the model. However, data from 1996 onward was collected after improvements 

to the State of Alaska reporting system had been established in 1995. A final decision on which timeframe 

to use for the trend analysis was made based on comparing models constructed using both timeframes.

Each model's ability to predict the last decade’s (2009-2019) spill numbers was then compared. A statistic 

0

2

4

6

8

10

12

14

16

18

20

196619681970197219741976197819801982198419861988199019921994199619982000200220042006200820102012201420162018

Number of Reported Spills

Year

Number of Spill by Size Class by Year

Class A > 1,000 bbl

Class B > 200 ≤ 1,000 bbl

Class C > 10 ≤ 200 bbl

Class D > 1 ≤ 10 bbl
28

called the root mean square error (RMSE) was used. RMSE is computed by averaging the squared 

deviations (predicted value - observed value) and then taking the square root of that figure. When 

comparing models, the one with the lowest RMSE is generally better. It was found that:

• The RMSE using a model built from 1988-2019 data was 2.6

• The RMSE using a model built from 1996-2019 data was 2.55

This difference between the two models is considered small, but it indicates that using a model built from

the smaller dataset (1996–2019) will not be inferior to the larger dataset of 1988–2019. Thus, it was 

decided that data from 1996–2019 (23 years) would be used for trend analysis and occurrence rate 

estimates. This decision was also supported by the following aspects of the operational context:

• Inconsistency in spill databases before 1995 (the current State of Alaska database was begun 

mid-year that year)

• Inconsistency in spill reporting and reporting requirements in early years

• Industry spill prevention practices improved after 1990 and thus spills since that time reflect 

current practices.

4.2 Annual Data vs. Monthly Data

It was also necessary to decide whether to focus on a model built using monthly data or annual data. 

Monthly data would have provided a much greater sample size and consequently more power if a valid 

model could be achieved. However, data on the number of spills per month has some features that make it 

unsuitable for modeling. First, the distribution is highly non-normal with most months having zero or a 

single spill occurring in them. Second, even those months with spills generally have a very small number 

of spills for statistical purposes. So, the interval variable ‘spills per month’ does not begin to approximate 

a continuous variable suitable for modeling. For annual data there were no years with zero spills. Most 

years had four or five spills, with a range from 1 to 11. In short, the distribution using annual data was 

closer to normal. A prerequisite for linear regression modeling is that the observed data will be normally 

distributed at each treatment level, in this case by calendar year. For this reason, we chose to use annual 

data for our modeling efforts.

Figure 7 compares the distributions of the monthly spills vs. annual spills.
29

Figure 7. Comparison of the frequency distribution for spills per month vs. spills per year for 

Cook Inlet spills, 1996–2019

4.3 Seasonal Variation in Cook Inlet Spill Rates

We examined the 1996–2019 spill data to determine whether or not there is a seasonal pattern inherent in 

Cook Inlet spills. More spills were recorded in late summer (July and August) than any other months. One 

possible explanation of this observation is that more maintenance and construction activities may occur 

during these months of long daylight and mild temperatures. We used the Kruskal-Wallis test to 

determine if this variation by month in the median number of recorded spills was statistically significant 

and found that it was not.4

Figure 8. Total number of oil spills by month in Cook Inlet, 1996–2019

 

4 Kruskal-Wallis chi-squared = 8.1564, df = 11, p-value = 0.6992

0

20

40

60

80

100

120

140

160

180

200

0 1 2 3 4 5 6 7 8 9 10 11

Number of Months

Spills per Month

Distribution of Spills per Month

1996 - 2019

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7 8 9 10 11

Number of Years

Spills per Year

Distribution of Spills per Year

1996 - 2019
30

4.4 Spill Trends by Year

Figure 9 shows the annual recorded number of spills plotted against the annual oil production for Cook 

Inlet from 1996–2019. The graph suggests that for this time range the number of spills roughly follows 

the production curve when annual values for each are plotted simultaneously. Clearly as production 

dropped over time, so did the total number of spills recorded. However, the 11 spills that occurred in 2019 

appears to be an anomaly.

Figure 9. Annual recorded number of oil spills plotted against the annual crude oil production for 

Cook Inlet, 1996–2019

Figure 10 shows the annual volume of recorded oil spills compared to annual oil production for Cook 

Inlet from 1996-2019. Spill volumes of near 500 bbl in the years 2004 and 2016 are anomalies. In 

contrast to the number of spills, the spill volume, however, does not closely follow the production profile. 

This indicated that predicting the number of spills will be easier than predicting the volume spilled.

 -

 2.00

 4.00

 6.00

 8.00

 10.00

 12.00

 14.00

 16.00

0

2

4

6

8

10

12

199619971998199920002001200220032004200520062007200820092010201120122013201420152016201720182019

Oil Production (million bbl)

Number of Spills

Number of Spills by Substance vs. Oil Production by Year

Spills

Production
31

Figure 10. Annual recorded volume of oil spills plotted against the annual oil production for Cook 

Inlet, 1996–2019

4.5 Spill Trends by Product Type

Figure 11 shows the yearly annual recorded number of crude and refined oil spills plotted against the 

annual oil production for Cook Inlet from 1996–2019. While both crude and refined spills vary 

considerably, the trend in crude oil spills more closely follows the trend in oil production. There is no 

readily discernable trend in the number of refined product spills.

 -

 2.00

 4.00

 6.00

 8.00

 10.00

 12.00

 14.00

 16.00

0

100

200

300

400

500

600

199619971998199920002001200220032004200520062007200820092010201120122013201420152016201720182019

Oil Production (million bbl)

Volume of Spills (bbl)

Volume of Spills vs. Oil Production by Year

Spills

Production
32

Figure 11. Annual recorded number of oil spills for crude oil and refined oil plotted against the 

annual oil production for Cook Inlet, 1996–2019

Figure 12 shows the annual volume of recorded crude and refined oil spills plotted against the annual oil 

production for Cook Inlet in the years from 1996-2019. Neither the crude nor the refined spill data 

follows the trend in annual oil production. The variability in refined oil spill volume appears much greater 

than for crude oil spill volume.

Figure 12. Annual recorded volume of oil spills for crude oil and refined oil plotted against the 

annual oil production for Cook Inlet, 1996–2019

 -

 2.00

 4.00

 6.00

 8.00

 10.00

 12.00

 14.00

 16.00

0

1

2

3

4

5

6

7

8

9

199619971998199920002001200220032004200520062007200820092010201120122013201420152016201720182019

Oil Production (million bbl)

Number of Spills

Number of Spills by Substance vs. Oil Production by Year

Crude Spills

Refined Spills

Production

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

0

100

200

300

400

500

600

199619971998199920002001200220032004200520062007200820092010201120122013201420152016201720182019

Oil Production (million bbl)

Reported Volume of Spills (bbl)

Volume of Spills by Substance vs. Oil Production by Year

Crude Spills

Refined Spills

Production
33

5 SPILL RATE OCCURRENCE ESTIMATES

The overall purpose of this project was to develop a method to estimate oil spill rates based on 

independent variables. This section describes the process and results of that effort.

5.1 Annual Number of Spills Over Time

5.1.1 Screening Independent Variables

The first step in building an occurrence rate estimation model is to screen independent variables. The 

initial screening was done using scatterplots and Pearson Correlation Coefficients. Scatterplots give an 

indication graphically of whether or not a relationship exists between two variables. That relationship 

may be linear, quadratic, or some other shape. The Pearson Correlation Coefficient, also referred to as r, 

measures the strength of the observed linear relationship. A relationship that is perfectly linear will have 

an r value of 1 or -1, the sign indicating whether the relationship is direct or inverse. A completely 

uncorrelated pair of variables would have an r of zero. In real situations the observed r lies between these 

extremes.

It was decided a priori that model building would start by including as potential independent variables all 

of those having a correlation relationship significant at 75% confidence (i.e. a p-value of 0.25 or less).

The dependent variables being screened were the total volume of oil spilled each year (Spill Vol.) and the 

total number of spills each year (No. Spills). The candidates for inclusion in a model as independent 

variables were: the annual volume (million cubic feet) of gas produced from gas wells (Gas Prod.), the 

annual volume (million barrels) of oil produced from oil wells (Oil Prod.), the annual volume (million 

barrels) of water produced from oil wells (Water Prod.), the average inflation adjusted price (US $) of 

Alaskan crude each year (Adj. Price), and the length (miles) of oil carrying pipelines (Pipeline Mi.) in the 

region each year.

Figure 13 presents a scatterplot matrix, distribution, and the Pearson Correlation Coefficient for each 

variable considered for inclusion in the modeling process.
34

Figure 13. Scatterplot matrix, distribution, and the Pearson Correlation Coefficient for each 

variable considered for inclusion in the Cook Inlet modeling process

Considering the p-values for the correlations between annual number of spill and each independent 

variable in Table 9, all Pearson Correlation Coefficient values are significant at the 90% confidence level, 

with the exception of gas production. See Table 10.
35

Table 10. Pearson Correlation Coefficient and p-value for independent variables related to annual 

number and volume of spills recorded in Cook Inlet, 1996–2019

Dependent Variable Annual number of 

spills

Independent Variable Pearson 

Correlation 

Coefficient 

p-value

Gas production 0.08 0.712

Oil production 0.48 0.018

Water production 0.47 0.019

Adjusted price -0.44 0.032

Pipeline miles -0.34 0.108

Overall, the linear correlations were significantly stronger between the potential independent 

variables and the number of spills observed than between the volume of oil spilled. This further 

reinforced the decision to focus the regression work on explaining the number of spills, not the 

volume spilled.

Natural gas production was the only variable that had a correlation coefficient with number of 

spills that was so weak that it was dropped from consideration.

5.1.2 Modeling Approach

We used the following approach to select a suitable model:

1. All candidate independent variables meeting the 0.25 p-value selection criteria were placed in 

a regression model as main effects (i.e. appearing alone as a term) and in all possible 2-way 

interactions (i.e. appearing as a term multiplying the variable with another variable).

2. The statistical software program “R” was used to develop regression models. R’s automatic 

step-wise variable selection procedure was run to find the model that minimized the Akaike 

Information Criteria (AIC statistic).

3. This procedure did not account for multicollinearity existing between the variables, so 

starting with the model suggested in the step-wise approach, a manual backward variable 

selection process was employed that removed terms based on which had the highest nonsignificant p-value and/or the highest Variable Inflation Factor (VIF statistic). The goal was 

to keep only models for which all terms had a VIF less than 10.

5.2 Predicting Annual Spill Numbers from Crude Oil Production Using 

Linear Regression

Applying this modeling approach to the Cook Inlet annual spill data resulted in a regression model with a 

single independent variable - Oil Production. Other independent variables were eliminated through the 

modeling process due to a high degree of multicollinearity between variables.

The resulting linear regression model was: N_tot = 2.1557 + Oil_Prod. x 0.3591

Where: N_tot = total annual number of spills for all spill types and classes

Oil_ Prod. = annual volume of crude oil produced from oil wells in million bbl

The relevant statistics for this model are shown in Table 11.
36

Table 11. Statistics for the linear regression model predicting annual spills number from oil 

production

Coefficients Estimate Standard 

Error t value p-value Significance

Intercept 2.1557 1.1454 1.882 0.0731

Oil Prod. 0.3591 0.1410 2.547 0.0184 0.05

Residual Standard Error 2.226 Degrees Freedom 22

Multiple r-squared 0.2227 Adjusted r-squared 0.1926

F-statistic 6.47 on 1 and 22 degrees of freedom

p-value 0.1838

The model indicated that for every increase of 1 MMbbl of oil production, the number of annual spills is 

expected to increase by 0.36 units (number of spills) for all spill classes. The model explains 22.77% of 

the variation observed in the annual number of spills. Figure 14 shows the model’s predicted value, the 

95% confidence interval, and the 95% prediction interval for the range of oil production values studied.

The confidence interval is the range that one would expect the mean value of the spill number to fall in 

95% of the time when a given production level occurs a large number of times. The prediction interval is 

the range that one would expect any one value of the spill number to lie in for a given oil production level 

95% of the time. 
37

Figure 14. Predicted value, 95% confidence interval, and 95% prediction interval for the expected 

number of all Cook Inlet oil spills for the range of oil production values studied

The model’s calculated multivariate power was 0.7199.

5 The power is adequate but not exceptional. This 

is attributed to the relatively small sample size.

The model had reasonably normally distributed residuals (i.e. predicted value - observed value), and the 

equal variance assumption for linear regression was satisfied. Both of these factors indicate the validity of 

the model.

The model’s chief weakness stems from the inclusion of an extreme outlier in the data: in 2019, at an 

annual oil production level of 5.2 MMbbl, there were 11 spills recorded. Some problematic points are 

almost always present when building regression models, and statisticians speak of outliers and leverage 

points which may exert undue influence on the coefficients of a model. In this model, the diagnostic 

software indicated that two outliers (point 2 - 1997 and point 24 - 2019) and one leverage point (point 1 -

 

5 Where u=1, v=22, f2=0.2948, significance level = 0.5 (i.e. 95% confidence)
38

1996). Only the 2019 point was believed to exert “undue influence” – i.e. significantly affect the value of 

the coefficients. We went back and examined the spills from 2019 and there was no practical reason for 

excluding the data, so it was kept in the model.

5.2.1 Predicting Large Spills

Since no Class A spill of greater than 1,000 barrels occurred during the 23-year timeframe chosen to 

develop occurrence estimates (1996–2019) it is not possible to predict their occurrence using the methods 

that we used to predict other spills. Table 8 in Section 3.2.5 shows four spills greater than 1,000 bbl were

identified in the history of the Cook Inlet oil fields. Another spill was recorded as 1,000 bbl in October 

1968, so there have been five large spills (defined here and by MMS/BOEM as ≥1,000 bbl) in or adjacent 

to Cook Inlet since its beginning. The time interval between these large spills ranged from less than eight 

months to 20 years. No time pattern was observed. At the end of 2019, 263 million barrels of crude oil 

had been produced since the last Class A spill almost 30 years before. 

Other researchers have used a Poisson distribution to estimate the probability of a large spill as a function 

of estimated total volume of production (Anderson et al., 2012, Ji et al., 2016). The distribution is based 

on the rate of large spills per Bbbl of oil production (lambda). 

As such the probability of a given number (n) of spills being observed can be calculated using the 

formula: P(n) = (lambda * t)^n * exp(-1 * lambda * t) / n!

Where: P(n) is the probability of a given number of large spills

lambda is the rate of large spills per give volume of oil production

t is the level of total oil production of interest

n! is the factorial of the given number large spills

For the purposes of this work the value of lambda was computed as the number of spills divided by the 

total production in Cook Inlet at the time that the last large spill occurred. The value of lambda is 

calculated as 4.45e-9 dividing 5 (the number of large spills observed through 1990) by the amount of oil 

produced up until that time6 (1.1 Bbbl). This is conservative because at the time of this report there are 5 

large spills total and oil production is now 1.4 billion barrels, which would result in a lambda of 3.63e-9. 

As such, the estimates presented here can be considered to be maximum estimates.

Note that the expected value of the number of spills for a given distribution is computed as:

E(n) = P(0) * 0 + P(1) * 1 + P(2) * 2 + P(3) * 3 ...

Table 12 shows the resulting expected number of large for various levels of oil production.

Table 12. Expected number of large spills over the total production volume of a Cook Inlet Oil

Production Level 

(Bbbl)

Expected Number of 

Large Spills

1.1 (1990 level) 5.0

1.4 (2019 level) 6.1

1.5 6.7

2.0 8.9

2.5 11.1

 

6 1958 to 1990
39

It is important to note that expected number was based on large spills over the lifetime of the field and 

that the lambda calculated for Cook Inlet is dependent on large spills that occurred over 30 years ago and 

thus does not reflect current oil spill prevention practices.

5.3 Predicting Annual Spill Volume from Crude Oil Production

Attempts to develop a regression model to estimate the annual volume of oil spills in Cook Inlet failed for 

two reasons. First, as seen in Figure 4, the distribution of the dependent variable, annual volume of spills 

has a strong positive skew, meaning that there are many more small spills and the mean value is highly 

influenced by a few larger spills. This suggests that the assumption of a normal distribution required for 

regression analysis is not appropriate. Second, the individual correlations of the independent variables 

with Spill Volume are all weak as seen in Table 13 and Figure 15. No variable has a significant linear 

relationship with the total volume spilled at 95% confidence level or even the 90% confidence level.

Figure 15. Distribution of volume of recorded oil spill in Cook Inlet, 1996–2019

Table 13. Pearson Correlation Coefficient and p-value for independent variables related to annual 

volume of spills recorded in Cook Inlet, 1996–2019

Independent Variable Pearson 

Correlation 

Coefficient

p-value

Gas Production 0.12 0.577

Oil Production 0.14 0.52

Water Production 0.25 0.244

Adjusted Price -0.30 0.152

Pipeline Miles -0.03 0.903

Still we attempted to use regression techniques to develop a model to predict annual oil volume spilled. 

Using an automatic variable selection approach, we developed a multivariate model containing all 

independent variables. However, with an adjusted R-square of 0.037, only about 4% of the variability in 

annual spill volume was explained by the model. The p-value was 0.3343 which is not significant at a 

0

1

2

3

4

5

6

1030507090

110130150170190210230250270290310330350370390410430450470490510

Count of Years

Reported Volume (bbl)

Frequency Distribution of Annual Volume of Cook Inlet Spills

1996 - 2019
40

90% or 95% confidence level and there was a high degree of multicollinearity. For all these reasons, the 

model was deemed unusable to predict annual spill volume.

An alternate simulation approach was used to arrive at estimates of spill volumes. This approach used a 

bootstrap technique to estimate mean spill volume for each size class and combined this with a Monte 

Carlo simulation to generate confidence intervals for the estimate of the number of spills of each class 

size. Bootstrapping is a commonly used statistical tool for establishing estimates of parameters along with 

the parameter’s expected distribution. This approach was used to estimate both the proportion and median

size of spills which would be expected to be Class B, C, or D. There were no Class A spills ( > 1,000 bbl) 

in Cook Inlet during the 1996–2019 period of interest, so statistical forecasting of this size spill is not 

possible using data from this time interval.

In a bootstrap model, the spills in the database are assumed to be random events with equal probability. 

The software then samples the dataset with replacement repeatedly for a sample of the same size as that 

actually observed. For each sample drawn, the proportion of spills of each spill size class is computed, as 

well as the median7 spill volume from the Class. The distribution of these sample statistics over a large 

number of trials represents the distribution that is expected to occur naturally. The results of the bootstrap 

estimate of the distribution of proportions for each spill class are shown in Figure 16.

A Monte Carlo simulation is used to estimate spill volume. A large number of trials was run in which 

randomly drawn records from the database were used to develop a model for number of spills. The 

prediction function generated an expected value for each trial. These spill numbers estimates are then 

combined with the estimated statistics for proportion and median size to come up with estimates of the 

number of spills expected from each size group and finally the total annual spill volume estimation. The 

procedure is outlined below:

1. The total number of spills expected is computed using a linear regression model. Multiple 

realizations from a Monte Carlo simulation yield a distribution of the expected number at a given 

production level. This allows for the estimation of a confidence interval.

2. The proportion by spill size class is estimated using the bootstrapped procedure.

3. The median size of a spill in each size class as determined by the bootstrap procedure is then 

applied.

The formula to estimate the total annual spilled volume is:

Vol_toty = Pred_N_toty x Prop_B x Med_B + Pred_N_toty x Prop_C x Med_C + Pred_N_toty x 

Prop_D x Med_D

Where: Pred_N_toty = total number of spills predicted for annual oil production level Y 

using the regression model with multiple realizations created via a Monte Carlo 

simulation

 

7 Because the distribution of spill volume is highly skewed, the median is a better estimate of the expected value 

than the mean.
41

Prop_X = Proportion of spills from Class X estimated using the bootstrapped 

procedure

Med_X=Median spill size of Class X estimated using the bootstrapped procedure

This method was used for five levels of oil production: 5, 7.5, 10, 12.5, and 15 million bbl per year. Table 

14 presents the predicted number of spills from each of these production levels taken from the linear 

regression model presented in Section 5.2. Table 15 presents the median spill size by class and 

corresponding 95% confidence intervals. Table 16 presents the estimated number of spills of each size 

class and the total annual volume of spills predicted for each level of oil production.

Figure 16. Bootstrap estimate of the distribution of proportions for each spill class

Proportion of Class B Spills

Proportion of Class C Spills

Proportion of Class D Spills
42

Table 14. Expected annual number of Cook Inlet spills for all size classes and corresponding 95% 

confidence interval for five levels of oil production

Oil Production 

(million bbl)

Expected Total 

Number of Spills

95% 

Confidence 

Interval

5 4 2.8 - 5.1

7.5 4.8 3.9 - 5.8

10 5.7 4.5 - 6.9

12.5 6.6 4.9 - 8.4

15 7.5 5.1 - 9.9

Table 15. Median Cook Inlet spill size by class and corresponding 95% confidence interval for 

Cook Inlet recorded spill 1996–2019

Class Median 

Spill Size 

(bbl)

B > 200 - ≤ 1,000 bbl 490

C >10 - ≤200 bbl 15

D >1 - ≤10 bbl 2.4

Table 16. Expected annual number of Cook Inlet spills and corresponding 95% confidence interval 

four size classes and five levels of oil production; and estimated total annual volume 

of spills predicted from the bootstrap/Monte Carlo model

Oil 

Production 

(million bbl)

Class B

>200 - <1,000 bbl

Class C

>10 - <200 bbl

Class D

>1 - <10 bbl All Classes

Expected 

Number 

of Spills

95% 

Confidence 

Interval

Expected 

Number 

of Spills

95% 

Confidence 

Interval

Expected 

Number 

of Spills

95% 

Confidence 

Interval

Total 

Annual 

Volume 

(bbl)

95% Confidence 

Interval

5 0.1 0 - 0.3 0.7 0 - 1.5 3.3 0 - 7.3 72 0 - 202.5

7.5 0.1 0 - 0.4 0.8 0.1 - 0.6 4 0.5 - 8 87 5.8 - 226.2

10 0.2 0 - 0.4 1 0.2 - 1.8 4.7 1.1 - 8.8 102 14.2 - 253.3

12.5 0.2 0 - 0.5 1.1 0.4 - 2 5.4 1.7 - 9.7 118 21.3 - 282.3

15 0.2 0 - 0.5 1.3 0.5 - 2.3 6.2 2.2 - 10.7 134 26.5 - 312.6

Figure 17 shows the predicted total annual volume of oil spilled for the five levels of annual oil 

production and associated 95% confidence intervals.
43

Figure 17. Bootstrap/Monte Carlo estimate of the predicted annual volume of Cook Inlet oil spilled 

vs annual crude oil production

5.4 Estimating Occurrence Rates by Oil Type

We now turn to estimating the occurrence rates for number and volume by oil type, either crude oil or 

refined oil.

5.4.1 Occurrence Rates for Number of Spills by Oil Type

Figure 11 depicts the number of recorded oil spills by substance type (crude and refined) versus the crude 

oil production by year. We attempted to develop models to predict the number of spills for each substance 

type.

Applying our modeling approach to the Cook Inlet annual crude oil spill data resulted in a regression 

model with Oil Production as the single independent variable.

The resulting linear regression model was: N_crude_tot = -0.1432 + Oil Prod. x 0.3209

Where: N_crude_tot = total annual number of crude oil spills

Oil_ Prod. = annual volume of crude oil produced from oil wells in million bbl

The relevant statistics for this model are shown in Table 17.

0

50

100

150

200

250

300

350

5 7.5 10 12.5 15

Annual Spill Volume (bbl)

Annual Oil Production (MMbbl)

Predicted Volume vs. Oil Production

Upper 95% Confidence Interval

Predicted Volume

Lower 95% Confidence Interval
44

Table 17. Statistics for the linear regression model predicting annual number of crude oil spills 

from oil production

Coefficients Estimate Standard 

Error t value p-value Significance

Intercept -0.1432 0.9482 -0.151 0.8813

Oil Prod. 0.3209 0.1167 2.750 0.0117 0.05

Residual Standard Error 1.844 Degrees Freedom 22

Multiple r-squared 0.2558 Adjusted r-squared 0.222

F-statistic 7.562 on 1 and 22 degrees of freedom

p-value 0.01169

The model indicates that for every increase of one MMbbl of oil production the number of annual spills is 

expected to increase 0.32 units. The model explains 26% of the variation observed in the annual number 

of spills. Figure 18 shows the model’s predicted value, the 95% confidence interval, and the 95% 

prediction interval for the range of oil production values studied.

Figure 18. Predicted value, 95% confidence interval, and 95% prediction interval for the expected 

number of crude oil spills for the range of annual oil production values studied
45

The occurrence model to predict annual number of crude oil spills is very similar to the model developed 

to predict annual number of all types of oil spills. 

Regression techniques were applied to develop a model to predict the annual number of refined product 

oil spills. A univariate model was developed with oil production as an independent variable, but with an 

R-square of 0.005, less than 1% of the variability in annual spill numbers for refined product was 

explained by the model. The p-value was 0.748 which is not significant at a 90% confidence level. For 

these reasons, the model was deemed unusable to predict annual numbers of refined spills. There was no 

significant linear relationship between annual number of refined oil spills and the oil production level.

The best method to predict the annual number of refined oil spills is the estimate of the mean number of 

refined oil spills which is 2.6 refined spills per year with a 95% confidence interval of 0.6 to 6.3. The 

skewness of the distribution is 1.06 and the kurtosis of the distribution is 0.96, so the distribution is close 

enough to normal to allow for a mean as an estimate. The reason that using the mean is the best method is 

that both the plot in Figure 11 and the regression against year indicate that the number of refined oil spills 

is relatively constant across time.

5.4.2 Occurrence Rates for Annual Volume of Spills by Oil Type

Figure 12 depicts the volume of recorded oil spill by substance type (crude and refined) versus the crude 

oil production by year. Neither the crude nor the refined spill data follows the trend in oil production, nor 

is the proportion of crude to refined spill volumes consistent over time or production level. We attempted 

to develop models to predict the number of spills for each substance type without success. There is no 

significant linear relationship between oil production and spill volume for either crude or refined oil. So,

an estimate of annual spill volume across all years is the best estimate.

The distributions for crude and refined annual oil spill volumes are highly skewed8, so the best estimate 

for annual spill volume by oil type is the median spill volume and the associated 95% percentile interval

as presented in Table 18.

Table 18. Median annual spill volume and 95% percentile interval by oil type for Cook Inlet spills 

1996–2019

Oil Type Median

Spill 

Volume 

(bbl)

Lower 5% 

Percentile 

Interval

Upper 95% 

Percentile 

Interval

Crude 6.3 0.0 63.2

Refined 13.0 1.3 453.1

 

8 Crude: kurtosis = 5.4 skewness = 2.3, Refined: kurtosis = 6.0 skewness = 2.6
46

6 CONCLUSIONS

6.1 Limitations and Challenges of Occurrence Models

The models developed here do not address the causality of the relationships noted between the number of 

spills and independent variables explored, merely that they were unlikely to have occurred by chance. 

Therefore, caution should be used when applying statistical models for predictions in dissimilar 

circumstances. While these occurrence models performed adequately for predicting spill numbers in 

similar oil fields during a similar timeframe, using them to predict spills in other places or times could 

lead to predictions outside the confidence intervals due to differences in technology, industry practices, 

regulation and oversight, or other circumstances.

Factors besides oil production volume contribute to oil spill occurrence rates as well. For example, 

because some spills are caused by human error, the number of work hours by people employed in the 

industry could be related to spill occurrence. Spill volume is also a function of the time it takes to detect 

and stop a leak, which can depend on both technology and operator protocols or decisions. Therefore, 

advances in technology may have a big effect on volume spilled.

At the same time that using spill data from a specific location is important, it will always be challenging 

to model oil spill occurrences based on historical spills. Oil spills, especially large ones, are generally rare 

occurrences so datasets are prone to being small. This is further confounded, as was the case in this study, 

by changes in reporting requirements and record keeping. Industry practices also change, due to required 

or voluntary use of best practices, along with new technology. If we assume that the efforts of regulators 

and industry to reduce the number and size of spills will improve spill prevention over time, occurrence 

estimation models based on historic spills may over-predict future spills.

6.2 Occurrence Estimates for Spill Number

A variety of regression models was applied to explore the most accurate predictive approaches that could 

be used to estimate the number of spills based on various production variables. In some cases, strong 

predictive models were identified. In others, simpler estimating methods proved as accurate as regression 

modeling. 

While several predictive models were developed for overall spill occurrence rates, there were challenges 

when similar approaches were applied to size category subsets. The best model for predicting the annual 

total number of spills was a linear regression based upon annual volume of oil produced in MMbbl. The 

model equation was:

N_tot = 2.1557 + Oil_Prod. x 0.3591

The best model for predicting the annual total number of crude oil spills was a linear regression based 

upon volume of oil produced. The model equation was:

N_crude_tot = -0.1432 + Oil Prod. x 0.3209

6.3 Occurrence Estimates for Spill Volume

We attempted to use regression to develop a model to predict total spill volume and spill volume by oil 

type without success. There is no significant linear relationship between any of the independent variables 
47

and the annual volume of oil spilled. So, an alternate approach was used to arrive at estimates of total spill 

volume using a bootstrap technique to estimate median spill volume for each size class and combined this 

with a Monte Carlo simulation to generate confidence intervals for the estimate of the number of spills of 

each class size. The resulting model was:

Vol_toty = Pred_N_toty x Prop_B x Med_B + Pred_N_toty x Prop_C x Med_C + Pred_N_toty x 

Prop_D x Med_D

This model predicts an annual spill volume of 87 bbl with a 95% Confidence Interval of 6 to 226 bbl at a 

7.5 MMbbl per year level of oil production.

6.4 Recommendations

Occurrence estimates could be improved by using more independent variables, though in order to be 

useful these need to be variables that can be estimated or planned on for the future. For example, the 

volume of refined product utilized to construct and operate the oil production infrastructure might be a 

better predictor of refined oil spill than total oil production itself.

Most crude oil spills are the result of the loss-of-integrity of some portion of the oil production 

infrastructure. Examining the spill record for an individual facility (e.g. pipeline, tank, or processing 

plant) and then comparing similar facilities to establish occurrence rates by facility type may provide 

additional insight into occurrence rates. Finally, as acknowledged, oil spill rate studies are limited by data 

quality. Reporting standards change over time and some data on potential independent variables are not 

recorded. 

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for US Department of the Interior, Bureau of Ocean Energy Management. OCS Study BOEM 2018-

006.

Alaska Department of Environmental Conservation, Division of Spill Prevention and Response. 2003. 

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Alaska Department of Environmental Conservation, Division of Spill Prevention and Response. 2007. 

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2019__Cook_Inlet_Units_Region_Map
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Anderson CM, Labelle RP. 1990. Estimated occurrence rates for analysis of accidental oil spills on the 

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50

8 APPENDICES
51

Appendix A: Collated Oil Spill Dataset
52

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-1 03/05/

66 1966 100.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-2 07/08/

66 1966 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-3 07/10/

66 1966 75.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Fire/

Explosion Other

CI-4 09/23/

66 1966 50.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-5 10/31/

66 1966 60.00

C Crude Oil Crude Oil Oil 

Exploration Oil Exploration Offshore Exploratio n

Unknown Human 

Error

Human Error: 

Unknown

CI-6 12/13/

66 1966 1400.0 0

A Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-7 1966 50.00C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Unknown Other Other

CI-8 05/02/

67 1967 7.50

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-9 08/11/

67 1967 1400.0 0

A Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-10 10/26/

67 1967 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Unknown

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-11 11/26/

67 1967 30.00

C Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Unknown Other Other

CI-12 02/29/

68 1968 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-13 03/28/

68 196

8 10.00D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown
53

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-14 03/31/

68 1968 2.60

D Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services Unknown Unknown Unknown

CI-15 04/11/

68 1968 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-16 04/17/

68 1968 315.00

B Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-17 04/17/

68 1968 15.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Unknown Unknown Unknown Unknown

CI-18 05/18/

68 1968 23.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-20 05/19/

68 1968 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-21 05/26/

68 1968 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-22 06/06/

68 1968 380.00

B Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-23 07/17/

68 1968 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-24 08/13/

68 1968 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-25 09/12/

68 1968 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-26 10/20/

68 1968 35.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Granite 

Point Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-27 10/23/

68 1968 1000.0 0

B Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other
54

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-28 10/30/

68 1968 2.00

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-29 11/06/

68 1968 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-30 11/07/

68 1968 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-31 12/17/

68 1968 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknow

n

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-32 02/20/

69 1969 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-33 04/18/

69 1969 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-34 04/22/

69 1969 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-35 06/04/

69 1969 124.00

C

Refined: 

Lube/Ge

ar Oil

Refined: Other Unknown Unknown Unknown Unknown Unknown Unknown Unknown

CI-36 07/06/

69 1969 40.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-37 03/03/

70 1970 10.00

D

Refined: 

Bunker 

oil

Refined: Other Support 

Dock

Support 

Facility/Service sOnshore Support 

Services Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-38 04/01/

70 1970 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-39 04/09/

70 1970 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Dumping Human Error: Other

CI-40 07/20

/

70 1970 5.00

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Granite Point Unknown Unknown Unknown
55

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-41 09/23/

70 1970 1.30

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Other Other

CI-42 10/27/

70 1970 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Flare Other Other

CI-43 01/07/

71 1971 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-44 03/07/

71 1971 8.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-45 04/12/

71 1971 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Unknown Unknown Unknown

CI-46 04/17/

71 1971 10.00

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay Unknown

Equipment 

Failure, 

Tank 

Failure

Human Error: 

Other

CI-47 1971 50.00C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical

Failure: Other

CI-48 02/14/

72 1972 10.00

D Crude Oil Crude Oil Vessel

Support 

Facility/Service sOffshore Support 

Services

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-49 08/09/

72 1972 10.00

D Crude Oil Crude Oil Oil 

Production

Oil Production Offshore Granite 

Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-50 10/16/

72 1972 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Human Error

Human Error: 

Unknown

CI-51 1972 3.90D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-52 02/22/

74 1974 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-53 02/22/

74 1974 119.00

C Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services Vessel

Collision/All

ision/Groun

ding

Human Error: 

Other

CI-54 03/10/

74 1974 10.00

D Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Cook Inlet Pipeline Unknown Other Other

CI-55 10/05/

74 1974 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Tank

Human 

Error, 

Overfill

Human Error: 

Overfill
56

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-56 05/05/

75 1975 5.00

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-57 07/14/

75 1975 2.00

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-58 08/03/

75 1975 3.00

D Refined: 

Diesel Refined: Diesel Oil Production

Oil Production Offshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-59 1976 2.40D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Unknown Unknown Unknown

CI-60 1977 5.00D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-61 1978 3.60D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-62 1978 10.00D Crude Oil Crude Oil Oil 

Production

Oil Production Offshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-63 1979 2.00D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown Unknown Unknown

CI-64 05/29/

86 1986 10.00

D

Refined: 

Bunker 

oil

Refined: Other Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

292

01/19/

87 1987 151.00

C Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore TradingBay Tank Human Error

Human Error: 

Other

CI-65 1987 50.00C Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-66 1988 2.00D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-67 1988 5.00D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Pipe or Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-68 1988 114.00C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill
57

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-69 11/14/

88 1988 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-70 1988 50.00C Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Unknown

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-71 1988 2.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Unknown Unknown

CI-72 1988 261.90B Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore Unknown Unknown Unknown Unknown

CI-73 1988 1.20D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Unknown Unknown Unknown

CI-74 1988 3.00D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-75 1988 5.00D Crude Oil Crude Oil Oil 

Exploration Oil Exploration Onshore Exploratio n

Unknown Unknown Unknown

CI-76 1988 1.20D Refined: 

Unknown Refined: Other Unknown Unknown Unknown Unknown Unknown Unknown Unknown

CI-77 12/08/

88 1988 2000.0 0

A Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Tank

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-78 1988 1.20D Refined:

Diesel Refined: Diesel Vehicle

Support 

Facility/Service sOnshore Support 

Services Vehicle Human Error

Human Error: 

Unknown

CI-79 1988 141.00C Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline Vessel Unknown Unknown

CI-

293

01/31/

89 1989 110.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Tank

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-80 1989 1.20D

Refined: 

Hydraulic 

Oil

Refined: Other Vehicle

Support 

Facility/Service sUnknown Support 

Services

Hydraulic 

System Unknown Unknown

CI-81 1989 1.20D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal
58

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-82 1989 1.50D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Unknown Pipe or Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-83 1989 2.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-84 1989 5.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-85 1989 2.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-86 1989 5.00D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-87 1989 58.00C Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-88 1989 60.00C Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Trading 

Bay Tank

Equipment 

Failure, 

Tank 

Failure

Human Error: 

Other

CI-89 1989 1.40D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-90 1989 2.40D

Refined: 

Turbine 

oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay Unknown Human Error

Human Error: 

Unknown

CI-91 1989 12.40C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Unknown Unknown Unknown

CI-92 1989 1.20D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point Unknown Unknown Unknown
59

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-93 1989 3.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Unknown Unknown Unknown Unknown

CI-94 1989 8.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point Unknown Unknown Unknown

CI-95 12/17/

90 1990

15.00C Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Offshore Cook Inlet Pipeline

Loading 

Arm

Collision/All

ision/Groun

ding

Human Error: 

Other

CI-96 1990 5.00D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-97 1990 2.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-98 1990 10.00D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-99 1990 2.40D

Refined: 

Unknown 

and 

water

Refined: Other Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

100

03/10/

90 1990 2300.0 0

A Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Cook Inlet Pipeline

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

101 1990 200.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

102 1990 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

103 1990 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical Failure: 

Valve/Seal
60

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

104 1990 3.00

D Crude Oil Crude Oil Oil 

Production

Oil Production Onshore Swanson 

River Unknown

Equipment 

Failure, 

Gauge/Site 

Glass 

Failure

Mechanical 

Failure: Other

CI-

105 1990 28.60

C Refined: 

Jet Refined: Other Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline Unknown

Equipment 

Failure,

Other

Mechanical 

Failure: Other

CI-

106 1990 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Kenai Pipeline Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

107 1990 1.50

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Tank 

Failure

Human Error: 

Other

CI-

108 1990 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

109 1990 1.20

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Unknown Unknown Onshore Support 

Services Unknown Other Other

CI-

110 1990 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Unknown Unknown

CI-

111 1990 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Unknown Unknown

CI-

112

08/29/

91 1991 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Unknown Tank Unknown Unknown

CI-

113

08/13/

91 1991 95.20

C Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services Other

Collision/All

ision/Groun

ding

Human Error: 

Other

CI-

114 1991 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

115 1991 18.00

C Crude Oil Crude Oil Oil 

Production Oil Production Unknown

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

116 1991 3.00

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Beluga 

River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other
61

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

117 1991 4.80

D Refined: 

Gasoline Refined: Other Oil Production Oil Production Onshore Trading Bay Tank

Equipment 

Failure, 

Gauge/Site 

Glass 

Failure

Mechanical 

Failure: Other

CI-

118 1991 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

119 1991 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error:

Overfill

CI-

120 1991 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown

Middle 

Ground 

Shoals

Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

121 1991 2.70

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

122 1991 1.30

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point Unknown

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

123 1991 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Unknown Unknown

CI-

124 1991 4.80

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Beluga 

River Unknown Unknown Unknown

CI-

125 1991 2.40

D Refined:

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOnshore Support 

Services Unknown Unknown Unknown

CI-

126 1991 15.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown Unknown Unknown

CI-

127 1991 7.10

D Crude OilCrude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Weld Failure

Mechanical 

Failure: Other

CI-

128

01/04/

92 1992 400.00

B Crude Oil Crude Oil Pipeline Oil Production Onshore Kenai 

Pipeline

Pipe or 

Line Freezing Mechanical Failure: Other

CI-

129

10/01/

92 1992 95.20

C Refined: 

Diesel Refined: Diesel Oil Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal
62

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

294

04/27/

92 1992 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

130 1992 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Flare Other Other

CI-

131 1992 1.20

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

132 1992 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

133 1992 220.00

B Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line Freezing Mechanical Failure: Other

CI-

134 1992 1.20

D Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

135 1992 1.50

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

136 1992 4.50

D Crude Oil Crude Oil Unknown Unknown Unknown

Middle 

Ground 

Shoals

Unknown Corrosion

Mechanical 

Failure:

Corrosion

CI-

137 1992 10.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

138 1992 2.40

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

139 1992 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

140 1992 1.20

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

141 1992 4.00

D Crude Oil Crude Oil Oil 

Exploration Oil Exploration Offshore Exploratio n

Unknown

Human 

Error

Human Error: 

Unknown
63

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

142 1992 39.70

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Human Error

Human Error: 

Unknown

CI-

143 1992 6.00

D Crude Oil Crude Oil Unknown Unknown Onshore Support 

Services Unknown Unknown Unknown

CI-

144 1992 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Unknown Unknown Unknown Unknown

CI-

145

04/20/

93 1993 47.60

C Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Unknown Unknown Human Error

Human Error: 

Unknown

CI-

146

05/17/

93 1993 50.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point Flare Other Other

CI-

147

05/25/

93 1993 2.40

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

148

11/08/

93 1993 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay

Pipe or 

Line Unknown Unknown

CI-

149

12/28/

93 1993 370.00

B Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Cook Inlet Pipeline Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

150 1993 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

151 1993 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Kenai Pipeline

Pipe or 

Line Freezing Mechanical Failure: Other

CI-

152 1993 378.00

B Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Cook Inlet Pipeline

Pipe or 

Line Other Other

CI-

153 1993 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Unknown

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

154

04/21/

93 1993 45.70

C Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Granite Point Unknown Human Error

Human Error: 

Unknown

CI-

155 1993 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Unknown Other Other

CI-

156 1993 126.10

C Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services Vessel

Collision/All

ision/Groun

ding

Human Error: 

Other

CI-

157

02/23/

94 1994 20.00

C Crude Oil Crude Oil Pipeline Oil Production Onshore Unknown Pipe or 

Line Freezing Mechanical Failure: Other
64

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

158

02/25/

94 1994 1.20

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Unknown Pipe or Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

159

04/06/

94 1994 100.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Tank Human 

Error

Human Error: 

Other

CI-

161

05/13/

94 1994 1.20

D Refined: 

Diesel Refined: Diesel Vessel

Support 

Facility/Service sOffshore Support 

Services

Vessel 

Transfer Unknown Unknown

CI-

162

08/01/

94 1994 25.00

C

Crude Oil 

and 

Produced 

Water

Crude Oil and 

Produced 

Water

Oil 

Production Oil Production Offshore Unknown Tank

Equipment 

Failure, 

Tank 

Failure

Human Error: 

Other

CI-

163

08/05/

94 1994 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Cook Inlet Pipeline Tank

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

164

08/09/

94 1994 2.00

D

Crude Oil 

and 

Produced 

Water

Crude Oil and 

Produced 

Water

Oil 

Production Oil Production Unknown Unknown Well

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

165

08/20/

94 1994 2.40

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Unknown Unknown Tank

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

166

10/09/

94 1994 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Pipe or Line Erosion Mechanical Failure: Other

CI-

167

11/18/

94 1994 15.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

168

12/26/

94 1994 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Unknown Unknown Pipe or Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

169

01/21/

95 1995 1.40

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Onshore Unknown Pipe or Line

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal
65

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

170

03/03/

95 1995 4.00

D

Crude Oil 

and 

Produced 

Water

Crude Oil and 

Produced 

Water

Oil 

Production Oil Production Onshore Granite Point Unknown

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

171

04/10/

95 1995 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Unknown Tank

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

172

04/22/

95 1995 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Well

Equipment 

Failure, 

Other

Mechanical 

Failure: Other

CI-

173

07/24/

95 1995 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

174

07/28/

95 1995 20.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

175

12/05/

95 1995 135.70

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore Unknown Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

176

01/10/

96 1996 2.40

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

177

04/20/

96 1996 2.00

D Crude Oil Crude Oil Transmissi

on Pipeline Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

178

08/09/

96 1996 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

179

10/05/

96 1996 11.90

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

180

12/20/

96 1996 1.30

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown
66

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

181

02/16/

97 1997 7.10

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

182

03/06/

97 1997 214.30

B Refined: 

Diesel Refined: Diesel Oil Production Oil Production Offshore Trading Bay Unknown Unknown Unknown

CI-

183

03/30/

97 1997 27.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

184

04/17/

97 1997 1.50

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Vehicle Human Error

Human Error: 

Unknown

CI-

185

06/22/

97 1997 2.40

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Onshore

West 

McArthur 

River

Unknown

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

186

08/18/

97 1997 5.00

D

Refined: 

Ballast 

water w 

oil

Refined: Other Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

187

08/26/

97 1997 1.20

D Refined: 

Diesel Refined: Diesel Oil Exploration Oil Exploration Onshore Exploratio n

Unknown Unknown Unknown

CI-

188

09/16/

97 1997 1.20

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

189

09/19/

97 1997 2.00

D Refined: 

Unknown Refined: Other Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

190

10/20/

97 1997 2.00

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore Swanson River Unknown Unknown Unknown

CI-

191

11/06/

97 1997 1.5

0D Refined: 

Diesel Refined: Diesel Support Dock

Support 

Facility/Service sOnshore Support 

Services Vehicle Human Error

Human Error: 

Unknown

CI-

192

02/06/

98 1998 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Unknown J TUBE Unknown Unknown

CI-

193

02/10/

98 1998 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Vehicle Human Error

Human Error: 

Unknown
67

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type

Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

194

02/28/

98 1998 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

195

05/17/

98 1998 20.00

C Crude Oil Crude Oil Transmissi

on Pipeline Oil Production Onshore

Middle 

Ground 

Shoals

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

196

05/17/

98 1998 10.00

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore

Middle 

Ground 

Shoals

Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

197

07/11/

98 1998 1.20

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Unknown

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

198

10/07/

98 199

8 1.30D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Unknown Unknown Unknown

CI-

199

11/19/

98 1998 1.10

D Crude Oil Crude Oil Transmissi

on Pipeline Oil Production Onshore Kenai Pipeline Unknown Human Error

Human Error: 

Unknown

CI-

200

01/06/

99 1999 60.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

201

02/13/

99 1999 8.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur

River

Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

202

03/14/

99 1999 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

203

06/18/

99 1999 1.30

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Corrosion

Mechanical 

Failure: 

Corrosion

CI-

204

07/09/

99 1999 2.60

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Unknown Corrosion

Mechanical Failure: 

Corrosion

CI-

205

10/23/

99 1999 12.00

C Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

206

05/31/

00 2000 5.80

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Unknown Human 

Error

Human Error: 

Unknown
68

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

207

07/26/

00 2000 1.20

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline Unknown Unknown Unknown

CI-

208

08/18/

00 2000 1.20

D Refined: 

Unknown Refined: Other

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Unknown Other Other

CI-

209

11/17/

00 2000 4.80

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Unknown Human 

Error

Human Error: 

Unknown

CI-

210

11/28/

00 2000 12.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

211

12/12/

00 2000 2.40

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Onshore Granite Point Unknown Unknown Unknown

CI-

212

01/27/

01 2001 4.80

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

213

07/31/

01 2001 123.80

C Refined: 

Diesel Refined: Diesel Transmission Pipeline Oil Production Onshore Kenai Gas Pipe or Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

214

11/14/

01 2001 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Other

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

215

11/27/

01 2001 4.80

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore

Middle 

Ground 

Shoals

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

216

12/04/

01 2001 4.80

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Redoubt Other Unknown Unknown

CI-

217

12/13/

01 2001 10.20

C Refined: 

Unknown Refined: Other Oil Exploration Oil Exploration Offshore Exploratio n

Unknown

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

218

01/29/

02 2002 1.60

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Well Unknown Unknown

CI-

219

03/04/

02 2002 4.00

D Refined: 

Unknown Refined: Other

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Tank Unknown Unknown
69

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

220

06/17/

02 2002 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

221

09/05/

02 2002 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

222

12/12/

02 2002 1.10

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI-

223

02/04/

03 2003 2.00

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Onshore Kenai Pipeline Other

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

224

02/25/

03 2003 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River Other Unknown Unknown

CI-

225

07/05/

03 2003 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay Unknown Unknown Unknown

CI-

226

08/17/

03 2003 15.00

C Refined: 

Gasoline Refined: Other Crude Oil Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

227

10/28/

04 2004 2.40

D Crude Oil Crude Oil Unknown Unknown Offshore Unknown Unknown Unknown Unknown

CI-

228

11/30/

04 2004 500.00

B

Refined: 

Natural 

Gas 

Liquids

Refined: 

Natural Gas 

Liquids

Oil

Production Oil Production Onshore Beaver Creek Tank Human Error

Human Error: 

Unknown

CI-

229

12/07/

04 2004 1.20

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Onshore Swanson River Tank

Equipment 

Failure, 

Gauge/Site 

Glass 

Failure

Mechanical 

Failure: Other

CI-

230

02/18/

05 2005 70.00

C Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

231

05/02/

05 2005 4.80

D Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

232

07/12/

05 2005 2.40

D Refined: 

Diesel Refined: Diesel Oil Production Oil Production Unknown Unknown Pipe or Line Crack Mechanical Failure: Other
70

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause

CI-

233

07/28/

05 2005 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Offshore Granite Point

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

234

12/15/

05 2005 1.00

D Refined: 

Asphalt Refined: Other Crude Oil Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Corrosion

Mechanical 

Failure: 

Corrosion

CI-

235

01/10/

06 2006 3.60

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

236

02/08/

06 2006 2.40

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

237

08/27/

06 2006 2.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

238

07/06/

07 2007 5.00

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

239

07/23/

07 2007 17.00

C Refined: 

Unknown Refined: Other

Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

240

09/11/

07 2007 24.20

C Refined: 

Diesel Refined: Diesel Oil Exploration Oil Exploration Onshore Exploratio n

Well Other Other

CI-

241

10/02/

07 2007 1.30

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Exploration Oil Exploration Onshore Exploratio n

Hydraulic 

System Unknown Unknown

CI-

242

04/16/

08 2008 10.00

D Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

243

11/13/

08 2008 2.00

D

Refined: 

Hydraulic 

Oil

Refined: Other

Natural 

Gas 

Production

Oil Production Offshore North 

Cook Inlet Vehicle

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

244

05/04/

09 2009 1.30

D Crude Oil Crude Oil Crude Oil 

Terminal Oil Production Onshore Kenai Pipeline

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause
71

CI-

245

12/19/

09 2009 1.40

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Exploration Oil Exploration Onshore Exploratio n

Hydraulic 

System

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

246

03/07/

10 2010 1.70

D

Refined: 

Natural 

Gas 

Liquids

Refined: 

Natural Gas 

Liquids

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Unknown Unknown Unknown

CI-

247

07/20/

10 2010 15.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

248

04/25/

11 2011 8.30

D Refined: 

Gasoline Refined: Other Oil Production Oil Production Onshore Trading Bay Tank Human Error

Human Error: 

Unknown

CI-

249

05/18/

11 2011 5.20

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

250

05/18/

11 2011 5.20

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

251

07/19/

11 2011 5.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

252

01/31/

12 2012 11.40

C Refined: 

Diesel Refined: Diesel Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline Tank External Factors Other

CI-

253

04/28/

12 2012 1.30

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Redoubt Drum(s) Human Error

Human Error: 

Unknown

CI-

254

07/11/

12 2012 3.30

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System Other Other

CI-

255

09/22/

12 2012 4.60

D

Refined: 

Hydraulic 

Oil

Refined: Other

Natural 

Gas 

Production

Oil Production Offshore North 

Cook Inlet Drum(s) Human Error

Human Error: 

Unknown

CI-

256

05/12/

13 2013 1.20

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay Tank Human Error

Human Error: 

Unknown

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause
72

CI-

257

07/30/

13 2013 2.60

D

Refined: 

Hydraulic 

Oil

Refined: Other

Natural 

Gas 

Production

Oil Production Onshore Unknown Hydraulic 

System

Equipment 

Failure, 

Gauge/Site 

Glass 

Failure

Mechanical 

Failure: Other

CI-

258

08/04/

13 2013 1.80

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore

West 

McArthur 

River

Tank

Equipment 

Failure, 

Gauge/Site 

Glass 

Failure

Mechanical 

Failure: Other

CI-

259

08/11/

13 2013 5.00

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore Swanson River Drum(s) Human Error

Human Error: 

Unknown

CI-

260

10/25/

13 2013 2.20

D Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Ninilchik Tank Human 

Error

Human Error: 

Unknown

CI-

261

04/17/

14 2014 25.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Other

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

262

04/27/

14 2014 4.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Other

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

263

06/14/

14 2014 1.70

D

Refined: 

Lube/Ge

ar Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

264

06/20/

14 2014 40.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

265

07/15/

14 2014 2.40

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System

Human 

Error

Human Error: 

Unknown

CI-

266

02/13/

15 2015 9.50

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore Swanson River

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

267

03/06/

15 2015 1.40

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Pipe or 

Line

Equipment 

Failure, 

Valve 

Failure

Mechanical 

Failure: 

Valve/Seal

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause
73

CI-

268

03/06/

15 2015 1.40

D

Refined: 

Natural 

Gas 

Liquids

Refined: 

Natural Gas 

Liquids

Oil 

Production Oil Production Onshore

West 

McArthur 

River

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI-

269

03/15/

15 2015 11.90

C Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Kenai Gas Tank Human 

Error

Human Error: 

Unknown

CI-

270

08/23/

15 2015 4.80

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

271

09/12/

15 2015 15.00

C Crude Oil Crude Oil Oil 

Production Oil Production Onshore Trading Bay

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

272

06/06/

16 2016 3.00

D Crude Oil Crude Oil Oil 

Production Oil Production Onshore

West 

McArthur 

River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI-

273

11/19/

16 2016 490.00

B Refined: 

Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore North 

Cook Inlet

Pipe or 

Line Unknown Unknown

CI-

274

12/19/

16 2016 1.50

D Crude Oil Crude Oil

Natural 

Gas 

Production

Oil Production Onshore North 

Cook Inlet

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI-

275

12/26/

16 2016 1.50

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

CI-

276

01/04/

17 2017 4.00

D Refined: 

Unknown Refined: Other Oil Production Oil Production Onshore Cosmopolitan

Pipe or 

Line

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

277

01/25/

17 2017 1.50

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System

Equipment 

Failure, 

Seal 

Failure

Mechanical 

Failure: 

Valve/Seal

CI-

278

01/29/

17 2017 1.30

D

Refined: 

Hydraulic 

Oil

Refined: Other Oil 

Production Oil Production Offshore Trading Bay

Hydraulic 

System

Equipment 

Failure, 

Unknown

Mechanical 

Failure: 

Unknown

ID Date Year Size

(bbl)

Size 

Class

Sub-

stance

Consolidated 

Substance

Facility 

Type

Consolidated 

Facility Type Location

Oil Field / 

Infra-

structure

Source Cause Consolidated 

Cause
74

CI27903/03/

17 2017 1.20 D Crude Oil Crude Oil Oil Production Oil Production Offshore Trading Bay

Pipe or 

Line Corrosion

Mechanical 

Failure: 

Corrosion

CI28001/24/

18 2018 10.50 C Refined: Diesel Refined: Diesel Oil 

Production

Oil Production Offshore Granite 

Point Tank Human Error

Human Error: 

Unknown

CI28103/04/

19 2019 2.70 D Crude Oil Crude Oil Oil Production Oil Production Onshore Cosmopolitan Tank

Human 

Error, 

Overfill

Human Error: 

Overfill

CI28204/15/

19 2019 5.00 D Crude Oil Crude Oil Oil Production Oil Production Onshore

Middle 

Ground 

Shoals

Pipe or 

Line Unknown Unknown

CI28305/23/

19 2019 1.20 D Crude Oil Crude Oil Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline Unknown Unknown Unknown

CI28405/28/

19 2019 2.40 D Crude Oil Crude Oil OilProduction Oil Production Onshore Unknown Well Unknown Unknown

CI28507/17/

19 2019 2.40 D Refined: Diesel Refined: Diesel

Natural 

Gas 

Production

Oil Production Onshore Beluga 

River Vehicle Human Error

Human Error: 

Unknown

CI28608/03/

19 2019 7.20 D Crude Oil Crude Oil Crude Oil Terminal Oil Production Onshore Cook Inlet Pipeline

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other

CI28708/08/

19 2019 1.20 D Refined: Unknown Refined: Other Oil Production Oil Production Onshore Swanson River Well Unknown Unknown

CI28808/13/

19 2019 2.40 D Refined: Unknown Refined: Other Oil Production Oil Production Onshore Swanson River Well Unknown Unknown

CI28910/01/

19 2019 7.10 D Refined: Diesel Refined: Diesel Support Dock

Support 

Facility/

Services

Onshore Support 

Services Unknown Other Other

CI29010/20/

19 2019 3.00 D Crude Oil Crude Oil Oil Production Oil Production Onshore Trading Bay

Pipe or 

Line

Human 

Error

Human Error: 

Unknown

CI29112/27/

19 2019 1.40 D Crude Oil Crude Oil Oil Production Oil Production Onshore Swanson River

Pipe or 

Line

Equipment 

Failure, 

Line Failure

Mechanical 

Failure: Other
75

Appendix B: Exposure Variable Datasets

Table B-1. Cook Inlet in-scope pipeline miles, 1960-2019

Years Pipeline 

Miles Years Pipeline Miles Years Pipeline Miles

1960 18.8 1980 286.3 2001 315.1

1961 18.8 1981 286.3 2002 327.9

1962 18.8 1982 286.3 2003 327.9

1963 18.8 1983 286.3 2004 327.9

1964 18.8 1984 286.3 2005 327.9

1965 41.5 1985 286.3 2006 332.7

1966 162.3 1986 305.7 2007 332.7

1967 214.9 1987 305.7 2008 332.7

1968 249.3 1988 305.7 2009 332.7

1969 249.3 1989 305.7 2010 332.7

1970 249.3 1990 305.7 2011 332.7

1971 271.0 1991 305.7 2012 332.7

1972 275.7 1992 305.7 2013 332.7

1973 275.7 1993 305.7 2014 332.7

1974 286.3 1994 305.7 2015 348.7

1975 286.3 1995 305.7 2016 348.7

1976 286.3 1996 305.7 2017 348.7

1977 286.3 1997 305.7 2018 352.2

1978 286.3 1998 305.7 2019 352.2

1979 286.3 1999 313.5

1960 18.8 2000 315.1
76

Table B-2. Adjusted Alaska North Slope crude oil pricing, 1996-2019

Years

Price 

(millions of 

dollars)

Adjusted Price

(millions of 

dollars)

1996 15.3341667 25.2046933

1997 14.7825 23.7598552

1998 8.45 13.3809404

1999 12.6283333 19.5068096

2000 23.6733333 35.4538201

2001 18.1841667 26.5014464

2002 19.3733333 27.764764

2003 23.77 33.341524

2004 33.1366667 45.2175597

2005 47.3116667 62.4392979

2006 56.9691667 72.8873095

2007 63.7991667 79.232205

2008 91.235 108.957409

2009 54.8366667 65.8183551

2010 72.1683333 85.3736891

2011 98.4725 112.942437

2012 98.345 110.527222

2013 95.8433333 106.124652

2014 86.4525 94.1685876

2015 41.3433333 44.9985385

2016 33.2575 35.710172

2017 44.9358333 42.7021524

2018 62.575 60.9194094

2019 57.27 56.7592687
77

Table B-3. Cook Inlet gas production per year, 1958-2019

Years Oil

(bbl)

Gas

(mcf)

Water

(bbl) Years Oil(bbl)

Gas

(mcf)

Water

(bbl)

1958 1989 - 194,090,185 143,159 

1959 1990 - 203,987,009 309,117 

1960 - 37,739 - 1991 - 197,336,158 242,486 

1961 - 214,718 - 1992 - 198,799,256 224,546 

1962 - 1,642,495 - 1993 - 189,891,574 99,059 

1963 - 8,002,308 - 1994 321 180,287,182 162,780 

1964 - 8,631,569 - 1995 162 179,190,365 140,882 

1965 - 8,312,234 - 1996 15 183,440,890 54,262 

1966 - 34,396,154 - 1997 - 179,233,348 59,061 

1967 - 40,005,807 - 1998 - 182,656,508 98,506 

1968 - 48,641,633 - 1999 - 177,223,490 119,999 

1969 2,497 76,054,167 - 2000 - 181,124,159 180,590 

1970 2,229 130,474,114 - 2001 - 193,920,605 177,204 

1971 1,119 125,267,279 - 2002 - 192,827,922 243,356 

1972 1,799 126,212,038 3,014 2003 - 195,636,474 506,737 

1973 1,036 123,954,869 2,800 2004 - 202,128,978 504,379 

1974 331 125,242,246 2,960 2005 - 205,829,839 829,280 

1975 877 138,109,178 2,903 2006 - 191,166,300 1,051,776 

1976 547 142,903,238 2,664 2007 1 162,804,610 711,470 

1977 430 150,351,112 3,208 2008 - 146,119,376 970,955 

1978 625 166,275,131 5,508 2009 - 133,896,300 886,289 

1979 383 172,308,231 3,826 2010 - 120,989,397 834,278 

1980 - 165,698,798 320,914 2011 - 111,335,111 1,006,790 

1981 - 180,472,551 14,479 2012 - 106,928,394 1,018,633 

1982 - 189,586,171 51,652 2013 431 90,612,468 1,367,908 

1983 - 196,212,558 47,204 2014 338 103,259,917 1,769,975 

1984 - 197,290,321 44,914 2015 638 96,321,416 1,964,557 

1985 - 204,257,471 67,252 2016 919 83,966,916 1,524,551 

1986 - 180,707,429 92,728 2017 1,017 81,938,839 1,262,904 

1987 - 184,662,427 229,360 2018 311 70,891,456 1,358,333 

1988 - 185,554,958 202,303 2019 297 64,177,324 1,269,635 
78

Table B-4. Cook Inlet oil production per year, 1958-2019

Years Oil

(bbl)

Gas

(mcf)

Water

(bbl) Years Oil(bbl)

Gas

(mcf)

Water

(bbl)

1958 35,754 5,643 283 1989 15,366,389 112,082,370 38,712,597 

1959 186,590 27,296 33,422 1990 11,147,416 107,531,650 30,576,153 

1960 557,999 99,176 11,508 1991 15,339,764 110,643,489 50,367,108 

1961 6,326,501 1,293,259 158,415 1992 15,179,279 110,273,127 50,439,615 

1962 10,259,110 1,914,055 294,133 1993 13,853,287 103,666,218 47,117,253 

1963 10,739,964 2,808,007 458,781 1994 15,561,658 130,892,139 50,615,808 

1964 11,053,872 3,233,232 1,253,159 1995 15,514,208 108,387,133 52,898,991 

1965 11,131,271 3,842,367 1,683,426 1996 14,586,281 82,372,508 51,820,943 

1966 14,364,432 6,822,597 2,114,821 1997 12,143,488 58,638,705 50,874,675 

1967 28,913,488 22,587,317 2,467,556 1998 11,801,635 43,381,126 49,768,194 

1968 66,145,673 51,210,051 3,246,604 1999 10,917,841 43,122,262 50,427,705 

1969 74,037,841 71,489,063 4,099,504 2000 10,718,184 37,860,296 51,639,919 

1970 82,414,675 87,889,247 6,370,585 2001 11,497,190 35,916,321 48,615,772 

1971 77,628,053 104,298,296 9,341,630 2002 11,283,636 18,030,781 49,449,635 

1972 72,639,686 98,434,976 11,248,886 2003 10,078,643 11,688,052 48,892,890 

1973 72,195,717 101,280,794 14,929,151 2004 8,207,600 6,355,064 44,633,568 

1974 70,073,989 104,574,885 17,065,332 2005 7,074,882 4,553,700 42,039,178 

1975 69,110,608 114,444,540 19,210,229 2006 6,228,885 3,436,591 40,260,914 

1976 62,404,340 123,747,811 20,981,345 2007 5,486,978 3,140,799 37,882,256 

1977 56,095,147 129,603,409 24,511,389 2008 4,769,533 2,893,736 37,451,687 

1978 50,131,629 127,525,293 25,402,876 2009 2,740,653 1,874,874 22,121,676 

1979 43,044,992 132,754,714 28,241,973 2010 3,739,107 2,404,347 32,982,194 

1980 36,246,519 134,230,280 32,258,740 2011 3,885,271 2,444,354 33,427,551 

1981 31,075,237 118,565,482 30,910,087 2012 4,023,894 2,749,154 32,012,876 

1982 27,411,153 119,534,948 29,861,736 2013 5,333,534 5,008,934 37,103,404 

1983 24,762,908 109,838,396 28,101,256 2014 6,245,120 6,358,641 48,404,657 

1984 21,983,532 108,130,486 30,402,206 2015 6,527,364 6,680,749 52,491,029 

1985 16,944,201 101,661,216 26,845,812 2016 5,628,097 7,023,563 49,746,162 

1986 17,580,258 104,166,508 32,861,957 2017 5,239,268 9,213,871 47,768,469 

1987 16,190,722 91,651,657 32,887,027 2018 5,606,516 12,218,500 50,143,706 

1988 15,715,951 110,729,879 34,254,187 2019 5,210,591 15,339,901 47,131,088 
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