Economics of Undiscovered Oil and Gas in the North Slope 

of Alaska: Economic Update and Synthesis

By Emil D. Attanasi and Philip A. Freeman 

Open-File Report 2009–1112

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For product and ordering information:

World Wide Web: http://www.usgs.gov/pubprod

Telephone: 1-888-ASK-USGS

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Suggested citation: 

Attanasi, E.D., and Freeman, P.A., 2009, Economics of undiscovered oil and gas in the North Slope of Alaska; 

Economic update and synthesis: U.S. Geological Survey Open-File Report 2009–1112, 59 p., available only online.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.

Cover: Map showing the Alaska North Slope assessment study area, which consists of Federal, Native, and State 

lands in the 1002 Area of the Arctic National Wildlife Refuge, the central North Slope, the National Petroleum Reserve 

in Alaska (NPRA), and the western North Slope (area west of the NPRA). See figure 1 in text.
iii

Contents

Abstract ......................................................................................................................................................................... 1

Introduction.................................................................................................................................................................... 2

Synopsis of Geologic Assessment................................................................................................................................. 4

Assessment Procedures ............................................................................................................................................ 4

Characteristics of Assessed Technically Recoverable Resources............................................................................. 5

Economic Approach......................................................................................................................................................13

Data ..........................................................................................................................................................................13

Scope........................................................................................................................................................................14

Economic Parameters...............................................................................................................................................15

Economic Assumptions.............................................................................................................................................16

Economic Procedures...............................................................................................................................................17

Cost Components .....................................................................................................................................................18

Transportation, Infrastructure, and Location Assumptions ....................................................................................18

Exploration, Development, and Production Costs .................................................................................................19

Exploration Costs...............................................................................................................................................20

Development Costs for Crude Oil Accumulations..............................................................................................20

Production Profiles and Operating Costs for Crude Oil Accumulations .............................................................21

Development Costs for Gas Accumulations.......................................................................................................21

Production Profiles and Operating Costs for Gas Accumulations......................................................................22

Economic Analysis Results...........................................................................................................................................22

Estimated Economic Oil in Undiscovered Oil Accumulations....................................................................................23

Estimated Economic Gas in Undiscovered Gas Accumulations ...............................................................................27

Conclusions and Limitations .........................................................................................................................................32

Acknowledgments ........................................................................................................................................................33

References Cited..........................................................................................................................................................33

Appendix 1. Volumes Associated with the Mean Estimate for Each Play in Each of the Four Assessment Areas .......37

Appendix 2. Allocation of Play Resources to Economic Zones.....................................................................................41

Appendix 3. Documentation of Cost Estimates.............................................................................................................45

Transportation Costs.................................................................................................................................................45

Feeder and Regional Pipeline Assumptions..........................................................................................................45

Field Development Costs..........................................................................................................................................49

Oil Field Design.....................................................................................................................................................49

Gas Field Design...................................................................................................................................................50

Drilling Costs .........................................................................................................................................................51

Facilities Costs—Oil and Gas Development..........................................................................................................52

Production Profile..................................................................................................................................................54

Oil Discoveries...................................................................................................................................................54

Gas Discoveries.................................................................................................................................................56

Operating Costs ....................................................................................................................................................56

Oil Fields............................................................................................................................................................57

Gas Fields .........................................................................................................................................................57

Appendix 4. Federal and Alaska Taxes ........................................................................................................................58

Royalties ...................................................................................................................................................................58
iv

Alaska State Taxes ...................................................................................................................................................58

Alaska’s Clear and Equitable Share Tax ...............................................................................................................58

Procedure ..........................................................................................................................................................58

Application to Project Analysis...........................................................................................................................59

Ad Valorem Tax.....................................................................................................................................................59

State Income Tax ..................................................................................................................................................59

State Conservation Tax.........................................................................................................................................59

Federal Income Taxes ..............................................................................................................................................59

Figures

[List includes figures in appendix 3]

 1. Map showing the Alaska North Slope assessment study area, which consists of Federal, Native, and 

State lands in the 1002 Area of the Arctic National Wildlife Refuge, the central North Slope, the 

National Petroleum Reserve in Alaska (NPRA), and the western North Slope (area west of the NPRA) ......... 3 

 2. Graphs of the size-frequency distributions of the estimated number of accumulations of undiscovered 

(A) oil and (B) gas associated with the 95th-fractile, mean, and 5th-fractile volume resource estimates 

in the Alaska North Slope assessment study area ........................................................................................... 9 

 3. Graphs of the size-frequency distributions of the estimated number of accumulations of undiscovered 

(A) oil and (B) gas at the mean volume resource estimate by study subarea in the Alaska North Slope 

assessment study area....................................................................................................................................10

 4. Map showing economic zones of the Alaska North Slope study area..............................................................13

 5. Summary graphs of undiscovered economic oil resources in (A) the entire North Slope study area and 

(B) the North Slope study area excluding the 1002 Area of the Arctic National Wildlife Refuge......................26

 6. Summary graph of undiscovered economic nonassociated gas resources in the Alaska North Slope 

study area........................................................................................................................................................32

A3–1. Map showing the partition of the 1002 Area of the Arctic National Wildlife Refuge into economic zones 

(A110 and A120) and a hypothetical, generalized regional pipeline transport system from Federal 

portions of the zones to processing facility areas and then to Pump Station 1 near Prudhoe Bay ..................48

A3–2. Graph showing percentage of water in oil production stream as a function of reservoir depletion for 

Kuparuk-type reservoirs...................................................................................................................................55

A3–3. Graph showing percentage of water in oil production stream as a function of reservoir depletion for the 

Alpine-type reservoirs in the National Petroleum Reserve in Alaska ...............................................................56

Tables

[List includes tables in appendixes 1, 2, and 3] 

 1. Aggregate estimates of the technically recoverable volumes of conventional oil, natural gas, and natural 

gas liquids based on the mean, 95th-, and 5th-fractile estimates of oil and nonassociated gas, 

respectively, for the North Slope study area..................................................................................................... 6

 2. Cumulative percentage distribution of estimated undiscovered technically recoverable oil in oil 

accumulations and nonassociated (NA) gas in gas accumulations by size class for the North Slope 

study area......................................................................................................................................................... 8

 3. Cumulative percentage distribution of mean estimates of undiscovered technically recoverable oil in oil 

accumulations and nonassociated gas in gas accumulations by size class for each North Slope study 

subarea............................................................................................................................................................11
v

 4. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices 

that offset costs of finding, developing, producing, and transporting the oil to market.....................................24

 5. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the North Slope study area excluding resources in the 1002 Area of the Arctic National Wildlife 

Refuge, available as a function of specified market prices that offset costs of finding, 

developing, producing, and transporting the oil to market ...............................................................................28

 6. Volumes of nonassociated gas and natural gas liquids (NGL) from undiscovered gas accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices 

that offset costs of finding, developing, producing, and transporting the gas to market...................................30

A1–1. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by play 

for the National Petroleum Reserve in Alaska .................................................................................................38

A1–2. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by play 

for the central North Slope...............................................................................................................................39

A1–3. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by play 

for the 1002 Area of the Arctic National Wildlife Refuge..................................................................................40

A1–4. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by play 

for the western North Slope.............................................................................................................................40

A2–1. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

National Petroleum Reserve in Alaska to economic zones N110, N120, N130, N210, N220, N230, 

N320, and N330, as identified in text figure 4 ..................................................................................................42

A2–2. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

central North Slope to economic zones C110, C120, and C130, as identified in text figure 4 .........................44

A2–3. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 1002 

Area of the Arctic National Wildlife Refuge to economic zones A110 and A120, as identified in text 

figure 4 ............................................................................................................................................................44

A3–1. Hypothetical pipeline system configuration distances and regional pipeline capacity by economic 

zone as identified in text figure 4 .....................................................................................................................47

A3–2. Estimated recovery per production well, in millions of barrels of oil (MMBO), for oil accumulations by 

economic zone within study subarea as identified in text figure 4....................................................................50

A3–3. Estimated recovery per production well, in billions of cubic feet of gas (BCF), for gas accumulations 

in any economic zone......................................................................................................................................51

A3–4. Estimates of oil field facilities investment costs per barrel of oil recovered by accumulation discovery 

size class for facilities located in the northernmost economic zone, C110, of the central North Slope............53

A3–5. Estimates of gas field facilities investment costs per thousand cubic feet of gas recovered by 

accumulation size class for facilities located in the northernmost economic zone, C110, of the central 

North Slope......................................................................................................................................................54

A3–6. Oil discovery production profiles used in the economic analysis .....................................................................55

A3–7. Gas discovery production profiles used in the economic analysis ...................................................................56

A3–8. Gas field unit production cost used in the economic analysis..........................................................................57
vi

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

 Length

foot (ft)

mile (mi)

0.3048

1.609

meter (m)

kilometer (km)

 Area

acre 4,047 2 square meter (m )

acre

square mile (640 acres)

0.4047

2.590

hectare (ha)

square kilometer

 Volume

barrel (bbl), (petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3) 

cubic foot (ft3) 0.02832 cubic meter (m3) 

Unit Abbreviations

bbl barrel of crude oil

BBL billions of barrels of liquids 

BBO billions of barrels of oil 

BCF billions of cubic feet 

BOE barrel of oil equivalent 

= 1 barrel of crude oil

 = 6,000 cubic feet of natural gas

= 1.5 barrels of natural gas liquids

Btu British thermal unit

MCF thousands of cubic feet 

MMBO millions of barrels of oil

TCF trillions of cubic feet
1

Economics of Undiscovered Oil and Gas in the North 

Slope of Alaska: Economic Update and Synthesis 

By Emil D. Attanasi and Philip A. Freeman

Abstract 

The U.S. Geological Survey (USGS) has published assessments by geologists of undiscovered 

conventional oil and gas accumulations in the North Slope of Alaska; these assessments contain a set of 

scientifically based estimates of undiscovered, technically recoverable quantities of oil and gas in 

discrete oil and gas accumulations that can be produced with conventional recovery technology. The 

assessments do not incorporate economic factors such as recovery costs and product prices. The 

assessors considered undiscovered conventional oil and gas resources in four areas of the North Slope: 

(1) the central North Slope, (2) the National Petroleum Reserve in Alaska (NPRA), (3) the 1002 Area of 

the Arctic National Wildlife Refuge (ANWR), and (4) the area west of the NPRA, called in this report 

the “western North Slope.” These analyses were prepared at different times with various minimum 

assessed oil and gas accumulation sizes and with slightly different assumptions. Results of these past 

studies were recently supplemented with information by the assessment geologists that allowed 

adjustments for uniform minimum assessed accumulation sizes and a consistent set of assumptions. The 

effort permitted the statistical aggregation of the assessments of the four areas composing the study area. 

At the mean values, 24 billion barrels of oil (BBO) was assessed in 179 oil accumulations and 

103 trillion cubic feet (TCF) of undiscovered nonassociated gas was assessed in 145 gas accumulations. 

The volumes of oil assessed for the NPRA and the 1002 Area of ANWR are about equal and together 

account for 86 percent of the oil assessed. Nearly all of the remainder of the undiscovered oil was 

assigned to the central North Slope study subarea. At the mean values, more than 61 percent of the 

natural gas in gas accumulations was assigned to the NPRA, 24 percent was assigned to the central 

North Slope subarea, 10 percent was assigned to the western North Slope subarea, and 4 percent was 

assigned to the 1002 Area of ANWR. For this aggregation, estimates of the 95th and 5th fractiles for oil 

in undiscovered oil accumulations are 17.4 BBO and 32.4 BBO, respectively, and for undiscovered 

nonassociated gas (that is, gas in gas accumulations) are 74.3 TCF and 135 TCF, respectively. 

The assessment aggregation predicts predominantly modest undiscovered accumulation sizes by 

North Slope standards. At the 95th fractile, only three accumulations of at least 500 million barrels of 

oil (MMBO), with total of 2.4 BBO, were predicted. At the mean and 5th-fractile estimates, oil in oil 

accumulations of at least 500 MMBO amount to about 5.2 BBO (in six accumulations) and 9.3 BBO (in 

nine accumulations), respectively. Most of these larger oil accumulations were assessed in the 1002 

Area of ANWR. Gas accumulations containing at least 3 TCF of gas account for only 4 percent of the 

assessed nonassociated gas at the 95th-fractile estimates, 12 percent of the gas at the mean estimate, and 

19 percent of the gas at the 5th-fractile estimate. 

This economic analysis is based on undiscovered assessed accumulation distributions 

represented by the four-area aggregation and incorporates updates of costs and technological and fiscal 

assumptions used in the initial economic analysis that accompanied the geologic assessment of each 

study area. Costs are in constant 2007 dollars. During 2007, refiner acquisition cost for crude oil ranged 
2

from $50.77 to $85.29 per barrel. Market prices for natural gas were valued at two-thirds the market 

prices of energy-equivalent volumes of crude oil, which has been the historical average. Results of the 

economic analysis are presented as separate cost functions associated with the mean and 95th- and 5thfractile estimates of technically recoverable oil in oil discoveries and gas in gas discoveries. Because a 

gas transportation system has not been built, the economic analysis of nonassociated natural gas 

assumed that there would be either a 10- or a 20-year delay between the expenditures for discovery of 

gas accumulations and their development and production that would access a gas pipeline to market. 

For the entire North Slope study area, at the mean estimate and a market price of $72 per barrel 

($8.00 per thousand cubic feet [MCF]), 21.0 BBO and 16.8 TCF of nonassociated gas are predicted to 

be economic to find, develop, and produce if one assumes constant 2007 costs and technology and the 

10-year delay between gas discovery and production for the market. At $72/barrel at the 95th- and 5thfractile estimates for oil in oil accumulations, the economic oil amounts to 14.5 BBO and 28.8 BBO, 

respectively. At $8/MCF, the economic nonassociated gas volumes at the 95th- and 5th-fractile 

estimates for gas in gas accumulations are 10.8 TCF and 31.9 TCF, respectively. 

Similarly, at the mean estimate, and a lower market price of $42/barrel ($4.67/MCF), the 

estimated volume of economically recoverable oil is 14.9 BBO; at the higher price of $108/barrel 

($12/MCF), the estimated volume of economic oil is 21.2 BBO. At $4.67/MCF, it is not economic to 

search for gas accumulations, but at $12/MCF, it is estimated that 62.4 TCF can be found and produced 

if there is no more than a 10-year delay between discovery and production for a market. Calculations 

based on the mean of the assessment indicate that the further delay of 10 years added to the initial 10-

year delay would reduce the economic nonassociated gas at a market price of $8/MCF to 14.4 TCF from 

16.8 TCF and at $12/MCF to 45.3 TCF from 62.4 TCF. 

This report is intended to place the geologic resource analysis into an economic context that is 

informative and easily understood by policymakers and decisionmakers. The scope of the economic 

analysis is general rather than site or prospect specific. The economic analysis is limited to the 

evaluation of general finding costs, development costs (including the costs of primary recovery and 

some aspects of secondary recovery), and the costs of transporting the product to market.

Introduction

The U.S. Geological Survey’s assessments of oil and gas in the North Slope of Alaska report a 

set of scientifically based estimates of undiscovered, technically recoverable quantities of oil and gas in 

discrete oil and gas accumulations that can be produced with conventional recovery technology. The 

assessors considered undiscovered conventional oil and gas resources in four areas of the North Slope: 

(1) the central North Slope (Garrity and others, 2005), (2) the National Petroleum Reserve in Alaska 

(NPRA) (Bird and Houseknecht, 2002), (3) the 1002 Area of the Arctic National Wildlife Refuge 

(ANWR) (Bird, 1999), and (4) the area west of the NPRA, called in this report the “western North 

Slope” (see fig. 1). These analyses were prepared at different times with various minimum assessed oil 

and gas accumulation sizes and with slightly different assumptions. Results of these past studies were 

recently supplemented with information by the assessment geologists that allowed adjustments for 

uniform minimum assessed accumulation sizes and a consistent set of assumptions (appendix 1). The 

effort permitted the statistical aggregation of the assessments of the four areas composing the study area 

shown in figure 1. 
3

Figure 1. Map showing the Alaska North Slope assessment study area, which consists of Federal, Native, and 

State lands in the 1002 Area of the Arctic National Wildlife Refuge, the central North Slope, the National Petroleum 

Reserve in Alaska (NPRA), and the western North Slope (area west of the NPRA).

Geologic assessments predict the numbers and sizes of conventional oil and gas accumulations 

that could occur in the study area. The assessed oil and gas volumes in these undiscovered 

accumulations are called technically recoverable because they represent resources thought to be 

recoverable with current technology and are not linked to costs or product prices. For three of the four 

areas (but not the western North Slope), prices and costs required to transform the estimates of 

undiscovered technically recoverable resources into estimates of producible reserves were presented in 

separate reports at the time of publication of the original assessments.1 The economic analysis prepared 

for this report is based on assessed resources represented by the four-area aggregation and updates in 

costs and technological and fiscal assumptions as of the end of 2007. 

This economic analysis contains estimates of the part of the distribution of undiscovered 

accumulations that could be commercially developed at particular market prices. The prices must be 

sufficient to repay incremental costs of finding, developing, and producing oil and gas and transporting 

them to a market. Although the cost functions that are constructed show cost and resource-recovery 

possibilities and are not supply functions as defined by economists, the data that underlie the functions 

commonly provide the basis for market-supply models. This analysis does not predict the revenues 

(bonus payments or rentals for leases), nor does it attempt to estimate the regional or national secondary 

economic benefits that may result as a consequence of future development of the resource.

This report is intended to place the geologic resource analysis into an economic context that is 

informative and easily understood by decisionmakers. Resources that are not economic at the range of 

 1

For the 1002 Area of the Arctic National Wildlife Refuge, see Attanasi (1999, 2005a,b); for the NPRA, see Attanasi 

(2003); and for the central North Slope, see Attanasi and Freeman (2005).
4

market prices considered are not expected to become part of the future reserve. The scope of the 

economic analysis is general rather than site or prospect specific. The economic analysis is limited to 

the evaluation of general finding costs, development and production costs (costs of primary recovery 

and some aspects of secondary recovery), and the costs of transporting the product to market. It should 

also be understood that the timing of the global industry’s pursuit of these resources is largely 

determined by the expected returns of competing opportunities elsewhere. 

In this report, the term “study area” refers to the North Slope assessment area (see fig. 1), and 

“study subareas” refer to the areas labeled in figure 1 as the western North Slope, the National 

Petroleum Reserve in Alaska, the central North Slope, and the 1002 Area of the Arctic National Wildlife 

Refuge. The geologic assessment procedures are first reviewed. A summary of the characteristics of the 

technically recoverable resources important for understanding the economic analysis is presented. 

Assumptions about markets, pricing, costs, and the technical relationships used in computing the 

incremental cost functions are then discussed. Results and interpretations of the economic analysis are 

presented in the concluding sections. 

Synopsis of Geologic Assessment

Assessment Procedures 

The North Slope geologic assessments are based on the concept of the petroleum play as the 

basic unit of assessment. A play is a set of known or postulated oil and (or) gas accumulations2 sharing 

similar geologic, geographic, and temporal properties, such as source rock, migration patterns, timing, 

trapping mechanisms, or hydrocarbon type (Baker and others, 1984). On the basis of geologic 

knowledge, available seismic data, and the findings of past North Slope exploration, the assessment 

geologists defined and described the known and prospective petroleum plays. A total of 62 potential 

plays were assessed. Across all plays, the uniform minimum accumulation size for oil accumulations 

assessed is 20 million barrels (MMBO) of recoverable oil, and for natural gas accumulations, the 

minimum accumulation assessed is 250 billion cubic feet (BCF) of recoverable nonassociated natural 

gas.

For each play, the assessment geologists assigned subjective probabilities to the occurrence of 

hydrocarbon accumulations to capture play and prospect risk. The play probability (commonly called 

play risk) is the probability of occurrence of at least one accumulation of minimum size (20 MMBO 

recoverable oil or 250 BCF recoverable gas). For hypothetical plays where the assessor was not 

confident of the occurrence of at least one accumulation as large as the threshold size, the play 

probability was the product of the occurrence probability of the three play attributes of charge, trap, and 

timing. 

A prospect probability was also assigned to each play. The prospect probability is the probability 

that any randomly chosen oil or gas prospect contains resources of at least 20 MMBO of technically 

recoverable oil or 250 BCF of technically recoverable gas. Prospect probabilities for oil and gas were 

generally different, but there was no attempt to assign different probabilities to individual prospects that 

might have been identified. The prospect probability may be computed as the product of the occurrence 

probabilities assigned by the geologist to the prospect attributes of charge, trap, and timing. The 

geologists also specified separate distributions for the number of oil and the number of gas prospects, as 

 2

Accumulations are classified as either oil or nonassociated gas on the basis of their gas-to-oil ratios. Those having at least 

20,000 cubic feet of gas per barrel of crude oil were classified as nonassociated gas; otherwise, the accumulations were 

classified as oil. Oil accumulations may have associated gas, and gas accumulations may have natural gas liquids.
5

well as reservoir depth. The number of accumulations (meeting the threshold size) is then the product of 

the number of prospects, the play probability, and the prospect probabilities. 

Data from available field studies, regional geophysical studies, knowledge about regional trends, 

and postulated regional geologic history allowed the assessment geologists to specify probability 

distributions for the reservoir attributes of (1) net reservoir thickness, (2) area of closure, (3) porosity, 

(4) trap fill, and (5) reservoir depth. Numerically simulated values from these distributions were 

combined with the engineering-based reservoir equation3 to predict size, depth, and characteristics of 

the undiscovered accumulations. These simulations, which were conditioned on the play and prospect 

probabilities, constituted the assessment results (see Schuenemeyer, 2005). 

In order to properly aggregate play results, when expressed as probability distributions to the 

study-area level, the covariance among plays must be specified. Pairwise dependencies between plays of 

the hydrocarbon charge, trap, and timing play attributes were assigned by the assessment geologists to 

all 62 plays. The ranked dependencies (high, medium, low) were assigned correlation values, and the 

values were averaged so that the pairwise dependency between plays was reduced to one correlation 

value. The resulting correlation matrix was transformed to a covariance matrix that was used in the 

aggregation of play results to the study-area level. Details of the aggregation procedure were discussed 

in Schuenemeyer (2005). 

Characteristics of Assessed Technically Recoverable Resources

Estimates of the total volume of resources are shown in table 1. At the mean values, 24.3 billion 

barrels of oil (BBO) was assessed in 179 oil accumulations and 103 trillion cubic feet (TCF) of 

nonassociated gas was assessed in 145 gas accumulations. At the mean, an additional 20.0 TCF of 

associated gas was estimated to be in undiscovered oil accumulations. The volumes of oil assessed for 

the NPRA and the 1002 Area of ANWR are about equal and together account for 86 percent of the oil 

assessed. Most of the remainder of the undiscovered oil was assigned to the central North Slope study 

subarea. More than 61 percent of the natural gas in gas accumulations was assigned to the NPRA. Table 

1 also shows that the North Slope study area aggregation estimates at the 95th and 5th fractiles for oil in 

undiscovered oil accumulations are 17.4 BBO and 32.4 BBO, respectively, and for nonassociated gas 

(that is, gas in gas accumulations), they are 74.3 TCF and 135 TCF, respectively. The individual studyarea volumes shown in the table for these fractiles represent each area’s contribution to the aggregate 

North Slope fractile estimate.4

In the study subareas shown in figure 1, the assessment included onshore Federal, State, and 

Native lands and offshore State areas. The area represented by the NPRA accounts for 52 percent of the 

 3

For each oil accumulation, for example, the simulated reservoir-attribute values included the following: (1) net reservoir 

thickness, t, in feet, (2) area of closure, ac, in thousands of acres, (3) porosity, p, as a decimal fraction, (4) trap fill, f, as a 

decimal fraction, and (5) hydrocarbon pore space, hps, as a function of p and Sw, where Sw is water saturation as a decimal 

fraction. The assessors provided estimates of the oil recovery factor, rfo, as a fraction of the in-place resources that are 

recoverable, and the formation volume factor, fvfo, was calculated as a function of trap depth and API gravity. Oil 

accumulation size, szo, in millions of barrels was calculated with the following equation:

szo = 7.758(t)(hps)(f)(rfo)(ac)/(fvfo) 

where hps = p(1-Sw).

For gas accumulations, the size, szg, in billions of cubic feet was computed as:

szg = 4.356(t)(hps)(f)(rfg)(ac)(fvfg)*10-8

where the recovery factor and formation volume factor were specifically defined for gas accumulations. 4

The area contributions to the aggregate North Slope study area 95th- and 5th-fractile estimates are generally not the same 

as the individual area’s 95th- and 5th-fractile estimates.
6

total study area under consideration, the central North Slope accounts for 31 percent, the western North 

Slope 13 percent, and the 1002 Area of ANWR 4 percent. 

Table 1. Aggregate estimates of the technically recoverable volumes of conventional oil, natural gas, and natural 

gas liquids based on the mean, 95th-, and 5th-fractile estimates of oil and nonassociated gas, respectively, for the 

North Slope study area. 

[NPRA, National Petroleum Reserve in Alaska; ANWR, Arctic National Wildlife Refuge; BBO, billions of barrels of oil; 

TCF, trillions of cubic feet of gas; BBL, billions of barrels of liquid. Data are from sources described in appendix 1]

Area

Oil accumulations Gas accumulations

Oil 

(BBO)

Associated 

gas 

(TCF) 

NGL

(BBL)

Nonassociated 

gas 

(TCF) 

NGL

(BBL)

Mean value estimate

NPRA 10.47 11.59 0.21 63.33 0.68

Central North Slope 3.41 3.60 0.08 25.10 0.29

1002 Area of ANWR 10.35 4.76 0.19 3.81 0.13

Western North Slope 0.08 0.05 0.00 10.36 0.12

 Total study area 24.30 19.99 0.48 102.60 1.22

95th-fractile oil estimate for study area

NPRA 8.55 9.50 0.17 62.77 0.68

Central North Slope 2.80 2.97 0.07 22.20 0.26

1002 Area of ANWR 5.92 2.67 0.10 3.19 0.08

Western North Slope 0.17 0.05 0.00 11.37 0.13

 Total study area 17.44 15.19 0.34 99.53 1.15

5th-fractile oil estimate for study area

NPRA 13.28 14.82 0.27 66.51 0.72

Central North Slope 3.87 4.12 0.09 26.80 0.31

1002 Area of ANWR 15.16 6.42 0.23 4.52 0.11

Western North Slope 0.09 0.04 0.00 10.44 0.11

 Total study area 32.40 25.40 0.60 108.27 1.25

95th-fractile gas estimate for study area

NPRA 9.87 11.01 0.20 45.60 0.49

Central North Slope 3.17 3.39 0.08 19.14 0.22

1002 Area of ANWR 10.39 5.15 0.23 3.47 0.11

Western North Slope 0.06 0.03 0.00 6.13 0.07

 Total study area 23.48 19.58 0.50 74.34 0.89

5th-fractile gas estimate for study area

NPRA 10.80 11.94 0.22 85.49 0.91

Central North Slope 3.68 3.86 0.09 33.09 0.38

1002 Area of ANWR 10.74 5.00 0.19 4.06 0.11

Western North Slope 0.06 0.04 0.00 12.40 0.14

 Total study area 25.28 20.85 0.50 135.03 1.54
7

The total volume of the assessed undiscovered technically recoverable resource (both oil and 

gas) is significant relative to the recoverable resources in past discoveries (21.1 BBO, 35.4 TCF) in the 

Alaska Arctic Petroleum Province (Houseknecht and Bird, 2006). The super-giant Prudhoe Bay field, 

giant Kuparuk River field, and several other fields in the 500-MMBO range account for most of that 

discovered volume. Houseknecht and Bird (2006) listed a total of 38 oil and gas accumulations 

discovered through 2005. At the mean estimate, the assessed undiscovered volumes were posited to be 

in 324 (179 oil, 145 gas) accumulations, suggesting that future finds will be much smaller than past 

discoveries. 

Table 2 shows the number of accumulations by size class and the corresponding percentage 

share of oil in oil accumulations and nonassociated gas in gas accumulations by size class. Figures 2A

and 2B display the assessed oil and gas accumulation size distributions posited for assessed 

undiscovered accumulations at the 95th-fractile, the mean, and the 5th-fractile estimates, respectively. In 

the undiscovered oil accumulation size distributions, more than 95 percent of the oil accumulations are 

smaller than 1 BBO. At the 95th fractile, only three accumulations with a total of 2.4 BBO have sizes 

greater than 500 MMBO. At the mean and 5th-fractile estimates, oil in accumulations of at least 500 

MMBO amounts to about 5.2 BBO (in six accumulations) and 9.3 BBO (in nine accumulations), 

respectively. 

Figure 2B shows the gas accumulation size distributions. The gas accumulation size distribution 

data show a relatively small proportion of the gas resource in accumulations in sizes greater than 3 TCF 

(when converted to barrels of oil equivalent (BOE); 3 TCF is about the same as 500 MMBO because 1 

BOE = 6,000 cubic feet of natural gas). Accumulations containing at least 3 TCF of gas account for 

only 4 percent of the assessed nonassociated gas at the 95th-fractile estimate, 12 percent of the gas at the 

mean estimate, and 19 percent of the gas at the 5th-fractile estimate (see table 2). 

The size-frequency distributions of undiscovered oil and gas accumulations for the mean 

estimates were disaggregated to show the size distributions of undiscovered oil and gas accumulations 

for each study area. Figure 3A and figure 3B display undiscovered size distributions for oil 

accumulations and nonassociated gas accumulations, respectively. Table 3 shows the numerical 

frequencies, as well as the cumulative volume distributions, for mean estimates.

At the mean estimates, the NPRA and the 1002 Area have assessed oil volumes that are almost 

identical (see table 1), but they have quite different oil accumulation size distributions (see table 3). 

About 43 percent of the assessed oil for the 1002 Area is assigned to accumulations of at least 500 

MMBO, whereas only 6 percent of the assessed NPRA oil is assigned to fields of that size. For the 

NPRA, the size class representing accumulations between 128 and 256 MMBO is posited to have the 

largest percentage (33 percent) of the oil. For the central North Slope, undiscovered oil accumulations 

of between 64 and 128 MMBO have the largest percentage (29 percent) of its assessed oil. 

The distributions of natural gas accumulations in the four subareas (see table 3) are also quite 

different. In the NPRA, 15 percent of the total mean resource (9.7 TCF) is assigned to accumulations of 

at least 3 TCF in size. Table 3 shows that the largest gas volume (17.2 TCF) for the NPRA is assigned 

to the size class representing accumulations from 768 BCF to 1.54 TCF, whereas the largest gas 

volumes for the western North Slope and for the central North Slope are assigned to the next smaller 

size class (384 to 768 BCF). The posited gas field sizes are only modest by Arctic standards, and the 

likelihood of commercial development will depend on how closely they are clustered and how close 

they are to transportation infrastructure when it is built. 
8

Table 2. Cumulative percentage distribution of estimated undiscovered technically recoverable oil in oil accumulations and nonassociated (NA) 

gas in gas accumulations by size class for the North Slope study area.

[MMBO, millions of barrels of oil; BBO, billions of barrels of oil; BCF, billions of cubic feet of gas; TCF, trillions of cubic feet of gas]

Size class

(MMBO)

95th-fractile estimate Mean estimate 5th-fractile estimate

Number of 

accumulations

Oil in

class

(BBO)

Cumulative 

percent

Number of 

accumulations

Oil in

class

(BBO)

Cumulative 

percent

Number of 

accumulations

Oil in

class

(BBO)

Cumulative 

percent

Oil in oil accumulations

4,096-8,192 0.0 0.0 0 0.0 0.1 0 0.0 0.0 0 

2,048-4,096 0.0 0.0 0 0.2 0.6 3 0.8 2.3 7

1,024-2,048 0.6 0.8 4 1.2 1.6 9 2.0 2.7 15

512-1,024 2.4 1.6 14 4.4 3.0 22 6.4 4.4 29

256-512 11.6 4.1 37 16.7 5.8 45 21.5 7.5 52

128-256 27.1 4.8 65 33.7 6.1 70 42.2 7.7 76

64-128 37.7 3.4 85 45.4 4.2 87 50.8 4.7 90

32-64 42.8 2.0 96 48.8 2.3 97 51.8 2.4 97

20-32 28.7 0.7 100 31.2 0.8 100 34.0 0.9 100

Size class

(BCF)

95th-fractile estimate Mean estimate 5th-fractile estimate

Number of 

accumulations

NA gas

in class

(TCF)

Cumulative 

percent

Number of 

accumulations

NA gas

in class

(TCF)

Cumulative 

percent

Number of 

accumulations

NA gas

in class

(TCF)

Cumulative 

percent

Gas in nonassociated (NA) gas accumulations

24,576-49,152 0.0 0.0 0 0.0 0.0 0 0.0 0.0 0

12,288-24,576 0.0 0.0 0 0.0 0.7 1 0.1 2.0 1 

6,144-12,288 0.1 1.3 2 0.4 3.4 4 1.2 10.3 9

3,072-6,144 0.4 1.7 4 2.0 8.4 12 3.2 13.6 19

1,536-3,072 5.2 10.4 18 8.3 16.9 29 11.7 24.1 37

768-1,536 20.3 20.9 46 25.8 27.1 55 31.1 33.2 62

384-768 46.7 25.0 80 55.2 29.5 84 61.7 33.4 86

250-384 49.1 15.1 100 53.6 16.5 100 59.8 18.4 100
9

Figure 2. Graphs of the size-frequency distributions of the estimated number of accumulations of undiscovered 

(A) oil and (B) gas associated with the 95th-fractile, mean, and 5th-fractile volume resource estimates in the Alaska 

North Slope assessment study area.
10

Figure 3. Graphs of the size-frequency distributions of the estimated number of accumulations of undiscovered 

(A) oil and (B) gas at the mean volume resource estimate by study subarea in the Alaska North Slope assessment 

study area. Oil assessed in the western North Slope (WNS) is so small that it would not be detectable in figure 3A. 

NPRA, National Petroleum Reserve in Alaska; CNS, central North Slope.
11

Table 3. Cumulative percentage distribution of mean estimates of undiscovered technically recoverable oil in oil 

accumulations and nonassociated gas in gas accumulations by size class for each North Slope study subarea.

[MMBO, millions of barrels of oil; BCF, billions of cubic feet of gas]

Size class Number of Oil in class Class Cumulative 

(MMBO) accumulations (MMBO) percent percent

National Petroleum Reserve in Alaska

4,096-8,192 0.00 0 0 0

2,048-4,096 0.00 1 0 0 

1,024-2,048 0.02 23 0 0 

512-1,024 1.05 646 6 6

256-512 9.34 3,205 31 37

128-256 19.29 3,483 33 70

64-128 21.79 2,022 19 90

32-64 18.26 860 8 98

20-32 8.91 231 2 100

Central North Slope

4,096-8,192 0.00 0 0 0 

2,048-4,096 0.00 5 0 0

1,024-2,048 0.01 19 1 1

512-1,024 0.10 62 2 3 

256-512 0.78 253 7 10

128-256 3.72 636 19 29

64-128 11.32 991 29 58

32-64 21.41 959 28 86

20-32 19.05 484 14 100

1002 Area of the Arctic National Wildlife Refuge

4,096-8,192 0.01 56 1 1

2,048-4,096 0.22 572 6 6 

1,024-2,048 1.16 1,587 15 21

512-1,024 3.22 2,263 22 43

256-512 6.51 2,318 22 66

128-256 10.65 1,929 19 84

64-128 12.08 1,120 11 95

32-64 8.78 419 4 99

20-32 2.94 77 1 100

Western North Slope

4,096-8,192 0.00 0 0 0 

2,048-4,096 0.00 2 2 2

1,024-2,048 0.00 4 6 8

512-1,024 0.01 5 6 14

256-512 0.02 8 11 24

128-256 0.08 13 18 42

64-128 0.20 18 24 65

32-64 0.39 18 23 89

20-32 0.34 9 11 100
12

Table 3. Cumulative percentage distribution of mean estimates of undiscovered technically recoverable oil in oil 

accumulations and nonassociated gas in gas accumulations by size class for each North Slope study subarea.—

Continued

[MMBO, millions of barrels of oil; BCF, billions of cubic feet of gas]

Size class Number of Gas in class Class Cumulative 

(BCF) accumulations (BCF) percent percent

National Petroleum Reserve in Alaska

24,576-49,152 0.00 0 0 0 

12,288-24,576 0.04 630 1 1 

6,144-12,288 0.36 2,801 4 5

3,072-6,144 1.52 6,316 10 15

1,536-3,072 5.50 11,272 18 33

768-1,536 16.35 17,218 27 60

384-768 30.85 16,614 26 87

250-384 27.43 8,483 13 100

Central North Slope

24,576-49,152 0.00 0 0 0 

12,288-24,576 0.00 7 0 0

6,144-12,288 0.03 186 1 1

3,072-6,144 0.22 894 4 4 

1,536-3,072 1.65 3,335 13 18

768-1,536 6.02 6,217 25 42

384-768 16.74 8,811 35 77

250-384 18.37 5,650 23 100

1002 Area of the Arctic National Wildlife Refuge

24,576-49,152 0.00 0 0 0

12,288-24,576 0.01 75 2 2

6,144-12,288 0.05 363 10 12

3,072-6,144 0.18 727 19 31

1,536-3,072 0.46 966 26 56

768-1,536 0.84 911 24 80

384-768 1.02 562 15 95

250-384 0.57 179 5 100

Western North Slope

24,576-49,152 0.00 0 0 0

12,288-24,576 0.00 7 0 0 

6,144-12,288 0.01 96 1 1 

3,072-6,144 0.11 430 4 5

1,536-3,072 0.67 1,334 13 18

768-1,536 2.63 2,752 27 45

384-768 6.60 3,517 34 79

250-384 7.24 2,224 21 100
13

The aggregation procedure used the play simulation data (of play realizations) for its basic data. 

This procedure allowed recovery of the individual play realizations and hence accumulation size 

distributions that contributed to the study area volume fractile estimate, so the economic analysis could 

utilize the assessment geologists’ allocations of the undiscovered resource to the economic zones 

defined and used in the earlier area studies; see figure 4 and appendix 2 of this report. The economic 

zones and resource allocations provide the conceptual basis for developing the costs associated with the 

existing and proposed product transportation system. 

Figure 4. Map showing economic zones of the Alaska North Slope study area. Zone prefixes derive from names 

of the subareas, which are shown in figure 1: W, western North Slope; N, National Petroleum Reserve in Alaska 

(NPRA); C, central North Slope; and A, 1002 Area of the Arctic National Wildlife Refuge.

Economic Approach 

Data

The geologic assessment data consisted of the play simulations (play realizations) associated 

with the North Slope study area 95th- and 5th-fractile volume estimates and the average of the play 

realizations that constituted the mean estimates. The simulation data include accumulation size, depth, 

reservoir net pay, and other characteristics. The data were partitioned into size and depth categories in 

order to characterize representative accumulations for the economic evaluation zones. 

Major components of oil and gas industry costs, such as drilling and service industry costs, are 

affected by oil and gas price levels and changes that commonly follow economic cycles. Between early 

2005 and July 2008, world market prices for crude oil moved from about $34 per barrel to nearly $150 

per barrel. The oil and gas industry typically faces increasing costs when price increases, particularly if 

it tries to rapidly increase output. 
14

For example, expansion of oil and gas production requires the development of new proved 

reserves.5 Net additions to proved reserves generally necessitate an increase in the annual drilling rate. 

In the short run, say 36 months from the base period, unless there are idle drilling rigs and experienced 

crews, additional drilling demand will translate into increases in day rates for crews and drilling rigs, 

sometimes without any additional drilling actually taking place. Eventually, rates will rise sufficiently to 

expand the capacity of the drilling industry by the commissioning of new drill rigs and training of new 

crews, which constitutes a long-run adjustment. The commissioning of new and technically advanced 

rigs will expand industry capacity, leading to stable or slightly reduced drilling costs. If oil prices 

decline, drilling typically declines and only the most efficient rigs and crews will remain in the industry, 

allowing a reduction in drilling cost. 

The recent rapid rise in oil prices from 2005 into 2008 produced significant cost escalation 

through most phases of operations. The amount of the increase from $34 per barrel in early 2005 to 

almost $150 per barrel in mid-2008 also drove all costs higher. Although the worldwide economic 

recession that seized most of the world’s economies by late 2008 reduced oil prices by about two-thirds, 

costs have not declined symmetrically. The purpose of the economic assessment is to estimate resource 

recovery volumes in relation to cost, based upon the long-run costs of the industries that service the oil 

and gas sectors. Some of the engineering and cost relationships used here were drawn from earlier 

economic studies prepared for the individual study areas (Attanasi, 2003; Attanasi, 2005a; Attanasi and 

Freeman, 2005) and sources referred to in these references. IHS QUE$TOR software (IHS Inc., 2007) 

and information from James Craig (Minerals Management Service, written communication, 2008) were 

used in calibrating and updating some costs. A detailed explanation of engineering relationships, cost 

assumptions, and fiscal relationships is provided in appendixes 3 and 4. 

Scope

Economic models are abstractions that characterize real economic systems and are typically just 

detailed enough to roughly approximate the outcomes of interactions between economic agents. Only 

the general direction and the approximate magnitude of the reaction of the system to price or cost 

change can be modeled. The results of the economic analysis are estimated costs of transforming 

undiscovered resources into discovered commercially producible volumes of oil and gas. Prices 

received by the operator must be sufficient to repay all investment expenditures, cover production costs 

including taxes, and still yield an acceptable return to investment; otherwise, the investment will not be 

undertaken. Costs include all expenditures incurred in finding, developing, and producing oil and gas 

resources and transporting them to market. The timing and costs associated with leasing that must 

precede exploration are not included. All these factors are highly uncertain because the posited oil and 

gas resources are still undiscovered. 

The cost functions are time independent and should not be confused with the firm’s supply or 

market-supply functions that relate marginal cost to production per unit time period. Because of the 

time-independent nature of the cost functions and the absence of market-demand conditions in the 

analysis, user costs and the opportunity costs of future resource use are not computed. 

At any given price, the oil and gas industry will allocate funds over a number of provinces and 

worldwide sources of supply in order to meet market demand at lowest costs. Observed market pricesupply relationships are the culmination of numerous supplier decisions over many projects and regions. 

 5

Proved reserves are estimated quantities of hydrocarbons that geologic and engineering data demonstrate, with reasonable 

certainty, to be recoverable from identified pools under existing economic and operating conditions. Under normal 

circumstances, less than 20 percent of proved reserves (and often much less) can be extracted annually to avoid reservoir 

damage.
15

Incremental cost functions represent costs that are computed independently of activities in other areas. 

However, these cost functions and the data that underlie the functions are commonly used as the basis 

for market-supply models. 

Economic Parameters

Technology and costs used in this analysis are assumed to represent those prevailing during the 

calendar year 2007.6

 As discussed above, the industries serving the oil and gas industry face erratic 

demands on services because of (1) volatile price changes related to shortfalls in production and (2) cost 

increases that are expected to be sustained despite new capacity that could modernize the service 

industries. The latter component is the primary basis for the cost assumptions in this economic analysis. 

The oil prices evaluated in this economic analysis are based on the landed market prices at the 

west coast of the conterminous United States, which is the primary destination of oil produced in 

Alaska. The natural gas prices evaluated are those for gas delivered to Chicago or similar destinations in 

the northern U.S. Midwest, which is the likely market for North Slope gas. All transportation costs are 

subtracted from the assumed market prices to calculate the wellhead oil and gas prices used for project 

evaluation. The market prices are assumed to be sustained, rather than an erratic spot price. The market 

price of natural gas liquids is assumed to be 75 percent of the per-barrel price of crude oil. 

The pipeline to transport natural gas to market in the conterminous United States has yet to be 

built. It is expected that the future gas pipeline will start near Pump Station 1 of the Trans-Alaska 

Pipeline System (TAPS) and proceed southward along the TAPS right of way until it is redirected to the 

southeast toward the Alberta Hub (AECO). The gas moving through the AECO market could reach U.S. 

markets through several northern border crossing points. Because of the uncertainty regarding the 

timing and access to shipping capacity of the future gas pipeline, this economic analysis includes data 

for two scenarios. For scenario 1, the assumption is that pipeline access for new discoveries will occur 

approximately 10 years from the time of discovery; for scenario 2, the assumption is that access will not 

occur until 20 years after discovery. The longer delay gives priority access for proven gas reserves in 

fields near the pipeline origin before new supplies are accepted from new outlying discoveries. For these 

scenarios, the expected net present values of commercial discoveries are discounted for the lag time 

between discovery and startup. To simplify the analysis, it is assumed that there is no direct cost to the 

operation as a result of delays (lease rental, storage, and reserve taxes) during the period between 

discovery and field development for market sales. 

In recent years, market prices for natural gas have been very volatile, ranging mostly from 

$5/MCF to $12/MCF and, in some markets, climbing even higher. However, historically the market 

valuation of gas relative to crude oil on a calorific heating basis has been discounted. For the gas prices 

that are used in the valuation of potential gas discoveries, unless otherwise stated, gas is valued at the 

market at two-thirds the value of oil based on calorific heating value or British thermal units (Btu). 

Because of the sheer size of the investment required for pipeline construction ($30 billion), the pipeline 

owners are likely to require long-term contracts of shippers and buyers, who, in turn, will agree to pay 

stable shipping fees (tariffs). Associated gas in new oil discoveries is not valued at the market but is 

assumed to be stripped of liquids and re-injected into the oil accumulation for pressure maintenance.7

 

Therefore, associated gas is not included in the gas cost functions. 

 6

As noted above, costs were adjusted to represent the stable component.

7

Associated gas could be recovered for sale when oil is depleted. However, the discounting for decades of delay in sales 

would significantly reduce its value so much that at the time of discovery, it would not be a significant factor in the decision 

to develop the oil discovery.
16

During 2007, domestic refiner acquisition cost for crude oil ranged from $50.77 to $85.29 per 

barrel. History has shown that when prices rise substantially and rapidly, it is unrealistic to assume that 

costs in constant dollars will match price increases and hold (Kuuskraa and others, 1987). In order to 

adjust cost to changes in prices, it is assumed that for market prices between $40 to $100 per barrel, the 

prevailing 2007 costs are unaffected by price volatility. Above $100 per barrel and below $40 per barrel, 

drilling, facilities, and operating costs would rise or decline as a fraction of the percentage price 

changes. Details of the price-cost adjustment are presented in appendix 3. 

Discounted cashflow analysis is specific to an individual project, and tax preference items that 

might be important from a corporate accounting stance are not considered in this general economic 

assessment. A minimum 12 percent after-tax required return is applied to all projects that are deemed 

economic. A one-eighth royalty is assumed to be paid to the owner of the mineral rights. In this study, 

the assumption is that $0.25 per barrel of produced oil is set aside by operators to fund abandonment 

costs for oil fields and $0.05/MCF is set aside to fund the abandonment cost of natural gas fields. All 

pipelines outside the petroleum lease unit are assumed to be operated as common carriers with estimated 

tariffs that must repay annual operating costs, State property tax, State and Federal income taxes, and a 

12 percent return to investors. 

The Alaska State taxes include a corporate income tax, ad valorem tax (property tax), and 

petroleum production tax (called ACES8

). Although the nominal corporate income tax rate is 9 percent, 

the effective tax rate is set by a complex formula based on the individual company’s production and 

sales. For planning purposes, State agencies use effective rates between 2 and 4 percent of net income. 

An effective corporate tax rate of 4 percent is used here. The State’s ad valorem tax is an annual charge 

equivalent to 2 percent of the economic value of equipment, facilities, and pipelines. The State 

petroleum production tax (ACES) replaced the severance tax and is described in appendix 4. Federal 

income tax provisions are as of the end of 20079 with an assumed rate of 35 percent of taxable income.

Economic Assumptions

For this study, it is assumed that industry will not invest in new projects unless the full operating 

costs, taxes, capital, and cost of capital can be recovered. The costs modeled here include all 

expenditures (except lease bonus and rental payments) that are estimated to be incurred by the industry 

in finding, developing, and producing the product and transporting it to market. Costs and market prices 

are modeled in constant 2007 dollars.10

Unless otherwise stated, it is assumed that all of the North Slope study area is available for

exploration and development for oil and gas. Currently, the central North Slope and parts of the NPRA 

are open on a limited basis. 

The cost functions presented are time independent, and so they are not the same as supply 

functions, which relate price to quantity per unit time. Because of the time-independent nature of the 

cost functions and the absence of market-demand conditions in the analysis, user costs or the 

opportunity costs of future resource use are not computed. 

 8

ACES is an acronym for Alaska Clear and Equitable Share tax (also see Alaska Department of Revenue, Tax Division, 

2007, for State tax explanation). 

9

According to the 1986 Tax Reform Act, 30 percent of development well drilling cost is classified as a tangible cost and 

therefore is capitalized over 7 years. Of the remaining 70 percent of drilling cost (that is, the intangible drilling costs), 30 

percent is depreciated over 5 years and the remaining 70 percent is expensed immediately.

10A primary motivation of this analysis is to capture economic implications of geologic uncertainty. Therefore the 

economic variables and engineering relationships used are expressed as point estimates rather than as probability 

distributions. 
17

Economic Procedures

A new discovery is commercially developable if the after-tax net present value of its 

development is greater than zero. Market prices, size, depth, regional costs, and co-product ratios 

determine whether a discovery will be commercially developable. The algorithm that calculated costs 

used the predicted size and depth distribution of undiscovered fields (at economic zone level) to 

compute quantities of resources that are commercially developable at various prices.

A finding rate model (Attanasi and Bird, 1996) was adjusted for each economic zone’s 

undiscovered oil and gas accumulations and was used to forecast the size and depth distribution of new 

discoveries from increments of wildcat drilling. The results of the forecasts drive economic field 

development and production processes to establish the expected aggregate value of new discoveries. 

Specifically, at a given price, the commercial value of developing a representative oil or gas 

accumulation in a specific size class and depth category is determined by the results of a discounted 

cashflow (DCF) analysis. 

The net after-tax cashflow consists of revenues from the production of oil less the operating 

costs, capital costs in the year incurred, and all taxes. All new discoveries from a size and depth 

category are assumed to be developed if the representative accumulation is commercially developable, 

that is, the after-tax DCF is greater than zero, where the discount rate (12 percent) represents the cost of 

capital and the industry’s required return. 

Production is assumed to stop (the economic limit is reached) when operator income declines 

below the sum of direct operating costs and the operator’s production-related taxes. Commercially 

developable accumulations are summed and represent an estimate of the potential reserves attainable 

from undiscovered accumulations at a given price and required hurdle or minimum rate of return. The 

results from this procedure do not imply that every accumulation determined to be commercially 

developable is worth exploring for because some accumulations are predicted by the finding rate model 

that will only meet the commercially developable threshold and not repay finding costs. 

Incremental units of exploration, development, and production effort will not be expended unless 

the revenues expected to be received from eventual production will cover the incremental costs, 

including a normal return on the incremental investment. Exploration continues until the incremental 

cost of drilling wildcat wells equals or exceeds the after-tax net present value of the commercial 

discoveries identified by the last increment of wildcat wells. For the last increment of hydrocarbons 

produced from a field, operating costs (including production-related taxes) per barrel of oil equivalent 

are equal to price. This procedure assures that for the commercially developable resources discovered 

by the last economic increment of wildcat wells, the sum of per-barrel finding, development, and 

production costs equals the wellhead price (price of oil to the field owner).11

When oil and gas accumulations occur in the same depth interval and geographic basin, 

exploration productivity is determined jointly by the expected oil and gas targets and their economic 

value. If the oil search finds gas and the gas discovery has a positive after-tax net present economic 

value, the operator might develop the gas or sell the discovery to an operator that will develop the 

discovery. However, if the gas discovery is of no value, the discovery is reported as a dry hole, with a 

show of gas. So, when oil and gas accumulations occur in the same exploration area and depth intervals, 

the expected number of wildcat wells depends on the net present values for both the oil and the 

 11The marginal finding costs as described here are calculated by dividing the cost of the last increment of wildcat wells 

(which is approximately equal to the sum of the after-tax net present value of all commercially developable fields discovered 

in that last increment of exploration) by the amount of economic resources discovered by the last increment of exploration. 

Marginal development and production cost per barrel (for the economic resources discovered in that last increment of 

exploration) are calculated by subtracting the marginal finding costs from the wellhead price.
18

nonassociated gas that are found. In such situations, the incremental cost function for oil discoveries 

depends on the value imputed to the gas finds and the incremental cost function for nonassociated gas 

depends on the valuation of the oil. This procedure of representing the joint nature of oil and gas 

exploration with finding rate functions has been applied to most U.S. provinces analyzed in the 

economic component of the 1995 U.S. Geological Survey’s National Oil and Gas Assessment (Attanasi, 

1998).

Cost Components

Transportation, Infrastructure, and Location Assumptions

Since 1977, oil produced in northern Alaska has been shipped via the Trans-Alaska Pipeline 

System (TAPS) to the Port of Valdez in southern Alaska and then transported by marine tanker to 

market. The peak flow for TAPS occurred in 1988 at just above 2.0 million barrels per day. For 2007, 

the TAPS flow rate averaged slightly less than 0.74 million barrels per day of oil and natural gas liquids. 

Pump capacity for the TAPS has recently been reduced so the apparent 1.25 million barrels per day of 

unused capacity is not currently available. The reduced capacity can be restored in the future if 

discoveries result in increased North Slope daily production. For this analysis, it is assumed that TAPS 

will be able to accept any additional supplies in the foreseeable future.

The TAPS tariff rates and marine transport rates to market are projected semiannually by the 

Alaska Department of Revenue, Tax Division (2007, 2008). The marine transport rate represents 

transport cost weighted by projected sales volumes to various destinations from Valdez to markets that 

have included the west coast of the conterminous United States, the Far East, and the U.S. Gulf of 

Mexico region. These rates are projected on an annual basis to 2018. The annual TAPS tariff forecasts 

by the Alaska Department of Revenue from 2006 through 2018 averaged $3.81 per barrel (nominal 

dollars). The State projections assumed that the announced future TAPS tariffs will be reduced by 

litigation. This litigation seeks to remove from the pipeline’s rate base certain expenditures claimed for 

pipeline enhancement. Alternatively, if one uses the 2008 rate of $4.87 as the basis for projecting 

required pipeline annual revenues and then divides the annual forecast of North Slope production to 

2018, the average tariff is $5.65 per barrel. Rather than assume that future tariffs will decline or that 

litigation will have no effect, we assume here that the 2008 tariff rate from Pump Station 1 to Valdez of 

$4.87 per barrel will prevail forward. The State projection of $1.61 per barrel for marine tanker 

transport to market is used, and so the total transport cost for crude oil to market is $6.48 per barrel. 

For the evaluation of nonassociated natural gas discoveries, it is assumed that gas will be 

transported from the discovery to a new gas conditioning plant located near Pump Station 1 of TAPS. 

The calculation of the gasline tariff from the gas conditioning plant to market is based, in part, on the 

data presented by TransCanada (TransCanada, 2007) in its application to the State of Alaska for a 

license under the Alaska Gasline Inducement Act. The analysis shows that the maximum transport tariff 

(including gas conditioning) to the Alberta Hub (AECO) is $2.58 per million Btu or $2.88/MCF if one 

uses the conversion factor in TransCanada’s application. At the time of the application, rates quoted to 

transport gas to the U.S. market (ConocoPhillips, 2007) averaged $1.06/MCF. These sources estimate 

the overall loss in sales gas volume transported due to fuel use at compressor stations to be about 11.5 

percent. The total cost of gas delivered to U.S. markets is then estimated to be $4.42/MCF. 

The study area was partitioned into the economic zones shown in figure 4. These zones were 

also defined in the earlier studies of the central North Slope (Attanasi and Freeman, 2005), the NPRA 

(Attanasi, 2003), and the 1002 Area (Attanasi, 2005a,b). The western North Slope constituted a single 

economic zone. Distances and the corresponding pipeline costs for field feeder lines and regional 
19

pipelines to transport oil or nonassociated gas to the Pump Station 1 area of TAPS were computed as 

levelized tariffs based on the assumption that the lines are operated as common-carrier pipelines. The 

assumed regional pipeline capacities, which in large measure determine the tariff rates from the 

discovery to the Pump Station 1 area or the inlet of the proposed gas conditioning plant, depend on play 

resource volumes that are computed with the play percentage allocation (see appendix 2) devised by the 

assessment geologists. 

The play percentage allocations to the various economic zones were based on the play outlines 

and supplemental information developed by geologists relating to the identification of gas- and oilprone areas within plays. A centroid for oil and a centroid for gas within each subarea were located on 

the basis of the play data. Transport costs to the Pump Station 1 area were computed by using the 

distance from each economic zone product centroid to Pump Station 1 or the location of the inlet of the 

proposed gas conditioning plant. Appendix 3 provides distances and pipeline capacities used for each 

zone. 

Exploration, Development, and Production Costs

North Slope exploration and field development procedures are designed to accommodate special 

requirements in the Arctic environment. Wildcat drilling typically occurs in the winter when temporary 

ice roads, ice pads, and ice airstrips can be constructed to support drilling activities. After the ice melts, 

there is no sign of the previous winter’s activity. Seasonal instability of the permafrost requires 

construction of permanent gravel pads to support production drilling rigs, wells, and facilities. 

Production wells are drilled directionally from the pads to target depths and lateral locations up to 

several miles away from the pad. Gravel drilling pads commonly accommodate as many as 40 well 

collars12 spaced at 10-foot intervals along with production equipment. Sidetrack and multilateral drilling 

of two or more wells using a single well collar enable more well completions to be made on individual 

drilling pads. 

The remoteness of the targets, the cold Arctic climate, and the absence of infrastructure result in 

high initial exploration and development costs compared with costs for conterminous U.S. locations. 

With stand-alone field development, produced oil is processed at the field’s central processing facility 

and the final product is transported from the periphery of the field to TAPS. Because commercial North 

Slope discoveries are large relative to onshore fields in other areas, the introduction of new technology 

to increase recovery produces large payoffs in volumes of oil, and so operators commonly introduce 

such technological innovations early in the development cycle. For example, the application of extended 

reach drilling has allowed production wells access to distant reaches of the reservoir (commonly up to 4 

miles), sometimes eliminating the need for additional drilling pads or allowing satellite pool 

development from existing drilling pads. Because of this technology, it is assumed that any offshore 

accumulation in State waters can be developed from onshore with extended reach wells or with an 

artificial gravel island in shallow waters, which would not substantially increase the stand-alone field 

cost.

Field development costs include well drilling and completion costs and the cost of facilities. 

Actual field development costs depend on site-specific characteristics of prospects. In the process of 

developing generic cost functions, a number of simplifying assumptions were made to keep the 

economic analysis tractable. The simulation realizations representing the undiscovered accumulations 

were grouped into accumulation size categories (table 2 provides the field size classes) and into 5,000-

foot depth intervals. The analysis also included the costs of vertical delineation wells for each 

 12The well collar is at the end of the steel well casing that protrudes at the surface of the drilling pad.
20

accumulation evaluated. Development costs for a representative accumulation for each size and depth 

class were estimated and tested against an economic screen. If the representative accumulation was 

tested to be economic, then all accumulations in that size and depth category were considered 

commercially developable.

The actual costs associated with exploration and development drilling and construction of 

facilities depend on distance to existing infrastructure, remoteness to coastal staging points, and costsharing arrangements. For each economic zone, cost factors were used to adjust costs for the remoteness 

and lack of infrastructure relative to the costs thought to prevail in coastal areas of the central North 

Slope economic zone. 

Exploration Costs

Costs of geologic and geophysical studies to locate exploration wells after a lease is acquired are 

included as part of the costs of wildcat wells. Wildcat well drilling costs were assumed to be twice the 

cost of drilling production wells for the particular economic zone. Nondrilling exploration expenditures 

include geologic and geophysical data collection after lease acquisition, scouting costs, and overhead 

charges. Nondrilling exploration expenditures,13 exclusive of lease bonuses and lease rental, were 

assumed to amount to 50 percent of the wildcat well drilling costs (Vidas and others, 1993) and were 

added to wildcat exploration expenditures.14 Exploration was evaluated in increments of 20 wildcat 

wells. Actual exploration and development costs will depend on site-specific characteristics of the 

prospects. Because play analysis does not provide specific locations, generic costs were used to model 

expenditures in each economic zone. Exploration costs are discussed further in appendix 3. 

Development Costs for Crude Oil Accumulations

The two principal field development cost categories are (1) drilling and completion costs of 

production and injection wells and (2) facilities costs. Research on new procedures, materials, and 

technology target these two categories to reduce cost and (or) increase productivity. The use of 

horizontal wells for all development at the Alpine field was designed to enhance well productivity and 

enabled the commercial development of an accumulation with a relatively thin pay interval by North 

Slope standards (Gingrich and others, 2001). Greater well productivity reduces the required number of 

wells for field development and also reduces the size and (or) number of drilling pads. Because of 

existing infrastructure in the central North Slope, opportunities exist for facility sharing, which reduces 

the economic threshold for smaller discoveries. 

Estimates of the number of development wells for a typical prospect assumed that the 

conventional well drainage area is 160 acres. Oil well recovery for the accumulation was based on the 

simulated reservoir attributes (see footnote 3 where the area variable, ac, is set equal to 160 acres). 

Details of the vertical well drainage area conversion for field designs with horizontal well 

configurations along with the procedure of drilling cost estimation are discussed in appendix 3. 

Facilities include drilling pads, flow lines from drilling sites, the central processing unit, and 

infrastructure required for housing workers and storage. Facilities design and costs depend on peak fluid 

flow rates and ultimately on the field size. Although little information is in the public domain, a version 

 13For potential prospect identification, the three-dimensional (3-D) seismic expense may range from $750,000 to $1 million 

per prospect (David Houseknecht, U.S. Geological Survey, written communication, 2005). The 3-D seismic surveys would 

follow lease acquisition and depend on an existing 2-D seismic survey that located the prospect. 14For example, a typical vertical development well at a measured depth of 7,500 feet costs $6 million. Total costs for a 

comparable wildcat well where nondrilling costs amount to 50 percent of drilling cost are about $18 million, that is, the 

product of $6 million x 2(wildcat factor) x 1.5(nondrilling cost factor). 
21

of the Northstar development plan, including development cost estimates, was submitted by British 

Petroleum Exploration to the State of Alaska for evaluation with its request for relief of profit-sharing 

provisions of the State lease (British Petroleum Exploration, 1996). Facilities costs were initially 

estimated for a region similar to the central North Slope by using the QUE$TOR cost analysis software 

(IHS Inc., 2007). These estimates were checked using facilities cost estimates inferred from published 

reports for other fields under development. The (step) cost relationship estimated for facilities is 

expressed as a per-barrel function of expected field recovery. 

As of the end of 2007, the eight oil fields developed on a stand-alone basis in northern Alaska 

were Prudhoe Bay, Kuparuk River, Lisburne, Milne Point, Endicott, Badami, Northstar, and Alpine. 

Other developed fields and pools have produced fluids (oil, gas, and water) transported to the central 

processing unit of a nearby stand-alone field for separation. Point McIntyre, Niakuk, North Prudhoe 

Bay, and West Beach all use the central processing facilities of the Lisburne field. Prudhoe Bay 

production facilities process production from Midnight Sun, Aurora, Polaris, Borealis, and Orion. The 

Kuparuk River field facilities also process production from Tabasco, Tarn, Meltwater, and Palm. The oil 

produced from the Oooguruk unit operated by independent Pioneer Natural Resources is processed at 

the Kuparuk facilities. 

The cost reduction from facility sharing depends on physical production configurations and on 

the relative bargaining strength of the satellite owner in comparison to that of the owner of the central 

processing facilities. The State of Alaska recognizes the importance of reducing capital barriers to 

attract entry of additional firms to the North Slope. The State has begun to study the potential regulatory 

issues of fair treatment of new entrants (Kaltenbach and others, 2004). Facilities sharing is assumed for 

smaller discoveries in economic zones C110 and N110 (see fig. 4). To minimize the development 

footprint within the 1002 Area, it is assumed that a shared oil and gas processing facility will be located 

just outside the 1002 Area (see Attanasi, 2005a,b, for details). Additional discussion is provided in 

appendix 3. 

Production Profiles and Operating Costs for Crude Oil Accumulations

The oil accumulation production profiles assumed in this study are based on historical 

experience and on information supplied to the State of Alaska Oil and Gas Conservation Commission 

for support of the operator’s development plans for new discoveries. Oil field operating costs include 

labor, supervision, overhead and administration, communications, catering, supplies, consumables, well 

service and workovers, facilities maintenance and insurance, and transportation. Annual field operating 

costs were estimated as a function of hydrocarbon and water fluid volumes and number of operating 

wells (Craig, 2002). The fluid volumes were projected annually from field production forecasts based on 

the relationship between water cut and cumulative production (see appendix 3). Water cut is the ratio of 

water produced compared to total volume of liquids produced. As fields are depleted, the water cut 

increases, thus increasing the per-barrel cost of oil processed. Operating cost estimates were reconciled 

with independently derived estimates using the QUE$TOR software. 

Development Costs for Gas Accumulations

Although large natural gas accumulations have been discovered on the North Slope, natural gas 

has not been developed for commercial export from the North Slope because there is no gas 

transportation system to market. Currently 8 billion cubic (BCF) feet per day is recovered during oil 

production operations and 200 BCF per year is used as fuel. When a gas pipeline is constructed [2018 at 

the earliest (TransCanada, 2007)], most of the gas supplied to fill the pipeline will likely come from 
22

Prudhoe Bay and other fields in the central North Slope subarea. Known gas reserves in these fields 

could supply the pipeline for at least 10 years if the nominal flow rate were 4.5 BCF per day. 

Without any direct information about technical relationships or cost for gas development on the 

North Slope, the cost estimates developed for this study relied on the data generated from the 

QUE$TOR software for facilities cost and operating costs. Facilities costs include gas dehydration and, 

if required, acid removal but not a natural gas liquids plant. This analysis assumes that natural gas 

liquids are transported with the gas from the field through feeder lines to the regional line. The highpressure regional lines transport gas and NGL in a dense phase to the gas processing facility to be 

constructed near Pump Station 1. 

Gas well drilling and completion costs are assumed to be similar to oil drilling costs on a 

measured depth basis. The number of wells required to produce a new gas discovery was computed by 

assuming a well drainage area of 640 acres (National Petroleum Council, 1981a,b). It was assumed that 

the natural gas wells would be vertical or slightly deviated, but not horizontal. 

Production Profiles and Operating Costs for Gas Accumulations

The production profiles of more recent discoveries in the Gulf of Mexico served as analogs for 

North Slope gas production. Development of North Slope gas discoveries is assumed to be delayed until 

the gas is marketable, that is, deliverable to market via a pipeline.15 Production data from the 

“Significant oil and gas fields of the United States” database (Nehring Associates, Inc., 2004) for recent 

Gulf of Mexico fields were analyzed to determine the relationship between peak production of gas fields 

and their known recoverable gas by field size categories. With these peak production rates as a function 

of estimated field size, it was assumed that field production would be held constant until 75 to 80 

percent of the field’s original reserves was produced. The phase of constant production is then followed 

by a rapid decline at a rate of 24 percent per year. Annual production costs relied upon cost estimates 

developed using the QUE$TOR software (IHS Inc., 2007). Details are presented in appendix 3. 

Economic Analysis Results 

It is reasonable for firms to expend funds to identify an asset that is expected to have value at 

some future but uncertain date. For the North Slope’s undiscovered gas, a key question is the timing of 

construction of the pipeline. There is the additional uncertainty about availability of pipeline capacity 

for transporting newly discovered gas to market. During a nominal 25-year life of the pipeline, which is 

planned to move 4.5 BCF per day, more than 41 TCF would be transported to market.16 Estimates of the 

volumes of proven, pipeline-quality, conventional gas resources on the North Slope are about 30 to 33 

TCF17 (Thomas and others, 2007). These volumes suggest that additional discovered gas reserves will 

be required to support a viable pipeline over its design life. 

To investigate the effect of timing on the economics of new gas developments, two scenarios 

were considered. Because the incremental cost functions are time independent, scenarios are static and 

represent resource costs at a single instant in time. For scenario 1, it is assumed that the scale and the 

regulation of the North Slope gas pipeline will allow some newly discovered gas to be transported to 

market upon completion of the pipeline. However, the current after-tax net present value of a new gas 

 15Even if a pipeline were operational by 2018, the earliest date discussed by TransCanada (2007), there might not be 

capacity for newly discovered gas until 10 years after the start of the gas pipeline’s operation. 

16A more likely useful life is 35 years (Thomas and others, 2007), during which the pipeline could transport more than 57 

TCF of gas.

17The largest accumulations of discovered gas are attributed to Prudhoe Bay and Point Thompson (Thomas and others, 

2007). At the current rate of gas usage (200 BCF per year), the gas available to the pipeline should be reduced by 2 TCF. 
23

discovery is discounted for the 10-year period of pipeline permitting and construction. Specifically, the 

analysis shows how the incremental cost function appears to an operator who explores in 2008 and must 

discount the net present value of a find (based on constant cost and the assumed North Slope gas 

pipeline tariff) for the 10-year lag time between disbursement of exploration cost and projected 

cashflow. The projected cashflow streams consist of expenses associated with exploration and 

development and net revenue from production. 

Scenario 2 assumes a 20-year delay between discovery and projected cashflow streams, but the 

development schedule is the same as that in scenario 1. Scenario 2 recognizes that the delay for 

development of newly discovered gas fields could lengthen an additional 10 years if proven gas in 

operating oil fields is given absolute priority for the capacity of the yet-to-be-built North Slope gas 

pipeline. 

Estimated Economic Oil in Undiscovered Oil Accumulations

Table 4 shows results of the economic analysis, where the recoverable volumes are related to 

costs for the entire area. The economic effects of geologic uncertainty are clear by observing the 

differences in the cost functions evaluated using the field size distributions associated with the 95th- and 

5th-fractile estimates (spanning the 90 percent confidence interval associated with the geologic 

estimates of technically recoverable resources). This set of estimates for the North Slope study area 

assumes that sales of gas in gas discoveries are delayed by 10 years after discovery and that there are no 

sales of associated gas in oil discoveries. At the mean assessment value estimate and a market price of 

$72 per barrel, it is estimated that 21.0 BBO of oil is economic to find, develop, and produce given the 

numerous assumptions discussed above. At $72 per barrel18 at the 95th- and 5th-fractiles estimates for 

assessed oil in undiscovered oil accumulations, the estimated economic volumes amount to 14.5 BBO 

and 28.8 BBO, respectively. Alternatively at a price of $42 per barrel, the estimated economically 

recoverable oil is 8.8 BBO, 14.9 BBO, and 21.5 BBO at the 95th-fractile, mean, and 5th-fractile 

estimates and, similarly, at $108 per barrel, the estimated economically recoverable oil is 15.5 BBO, 

22.2 BBO, and 30.3 BBO, respectively. 

Figure 5A shows the associated functions graphically. The vertical lines indicate the assessed 

volumes of technically recoverable oil. The predicted volume resulting from the $30-per-barrel increase 

in prices from $42 to $72 per barrel was much greater than the volume response from $72 to $108 per 

barrel. However, over the long term, sustained high prices are likely to lead to improvements in 

recovery technology that will improve the recovery factor and shift the vertical lines to the right.

 18The year of 2008 has been chaotic in terms of oil prices. EIA projects average refiner acquisition price for 2008 to be just 

over $72 per barrel (Energy Information Administration, 2008).
24

Table 4. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices that offset costs 

of finding, developing, producing, and transporting the oil to market. 

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of undiscovered oil accumulations based on the North 

Slope study area aggregation consisting of all State, Federal, and Native lands in the National Petroleum Reserve in Alaska 

(NPRA), the central North Slope, the 1002 Area, and the western North Slope. Results of computations shown in the table 

are based on the assumption that sales of gas in gas discoveries are delayed 10 years. Prices are in 2007 dollars. Asc. gas, 

associated gas; $/bbl, dollars per barrel; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; BBL, billions of 

barrels of natural gas liquids]

Oil 

price

($/bbl)

95th-fractile estimate Mean estimate 5th-fractile estimate

Oil 

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

Oil 

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

Oil 

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

27 2.71 0.92 0.02 5.63 1.83 0.03 10.02 3.27 0.06

30 3.11 1.07 0.02 7.48 3.23 0.07 12.31 4.72 0.11

33 5.43 3.31 0.07 10.14 5.79 0.14 15.50 7.15 0.18

36 6.32 4.12 0.08 11.43 6.97 0.18 17.01 8.36 0.22

39 7.22 4.93 0.11 12.95 8.50 0.22 19.18 10.13 0.26

42 8.78 6.23 0.13 14.93 10.67 0.27 21.51 12.14 0.30

45 10.09 7.33 0.15 16.26 12.01 0.31 23.63 14.08 0.34

48 11.45 8.38 0.16 17.44 13.30 0.33 24.63 15.03 0.36

51 11.85 8.76 0.17 18.19 14.06 0.35 25.51 15.90 0.38

54 12.29 9.10 0.17 18.97 14.94 0.37 26.32 16.56 0.40

57 13.02 9.70 0.18 19.41 15.44 0.38 26.91 17.09 0.41

60 13.21 9.91 0.19 19.76 15.82 0.39 27.59 17.77 0.42

63 13.68 10.34 0.19 20.39 16.46 0.40 27.93 18.06 0.43

66 13.75 10.40 0.19 20.66 16.78 0.41 28.33 18.39 0.44

69 14.28 10.85 0.20 20.78 16.91 0.41 28.52 18.55 0.44

72 14.47 11.04 0.20 21.03 17.18 0.42 28.76 18.80 0.45

75 14.57 11.13 0.20 21.21 17.37 0.42 29.15 19.12 0.45

78 14.78 11.30 0.20 21.40 17.56 0.43 29.31 19.24 0.46

81 14.80 11.32 0.20 21.42 17.59 0.43 29.40 19.33 0.46

84 14.99 11.48 0.21 21.66 17.80 0.43 29.50 19.40 0.46

87 15.08 11.54 0.21 21.86 18.00 0.43 29.74 19.59 0.46

90 15.24 11.67 0.21 21.88 18.02 0.43 29.81 19.65 0.46

93 15.26 11.68 0.21 21.98 18.12 0.44 29.93 19.74 0.46

96 15.34 11.74 0.21 22.10 18.22 0.44 29.98 19.78 0.47

99 15.47 11.83 0.21 22.14 18.25 0.44 30.03 19.82 0.47

102 15.48 11.83 0.21 22.18 18.29 0.44 30.15 19.89 0.47

105 15.49 11.84 0.21 22.19 18.30 0.44 30.20 19.92 0.47

108 15.50 11.85 0.21 22.19 18.30 0.44 30.28 20.00 0.47

111 15.55 11.90 0.21 22.25 18.34 0.44 30.33 20.05 0.47

114 15.61 11.94 0.21 22.29 18.38 0.44 30.34 20.05 0.47

117 15.70 12.00 0.21 22.40 18.48 0.44 30.35 20.06 0.47

120 15.77 12.06 0.21 22.48 18.55 0.45 30.42 20.11 0.47

123 15.77 12.06 0.21 22.48 18.56 0.45 30.42 20.11 0.47

126 15.81 12.08 0.21 22.49 18.56 0.45 30.51 20.17 0.47

129 15.81 12.08 0.21 22.52 18.58 0.45 30.54 20.18 0.47

132 15.87 12.11 0.21 22.53 18.59 0.45 30.61 20.23 0.48
25

Table 4. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices that offset costs 

of finding, developing, producing, and transporting the oil to market.—Continued

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of undiscovered oil accumulations based on the North 

Slope study area aggregation consisting of all State, Federal, and Native lands in the National Petroleum Reserve in Alaska 

(NPRA), the central North Slope, the 1002 Area, and the western North Slope. Results of computations shown in the table 

are based on the assumption that sales of gas in gas discoveries are delayed 10 years. Prices are in 2007 dollars. Asc. gas, 

associated gas; $/bbl, dollars per barrel; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; BBL, billions of 

barrels of natural gas liquids]

Oil 95th-fractile estimate Mean estimate 5th-fractile estimate

price Oil Asc. gas NGL Oil Asc. gas NGL Oil Asc. gas NGL

($/bbl) (BBO) (TCF) (BBL) (BBO) (TCF) (BBL) (BBO) (TCF) (BBL)

135 15.87 12.11 0.21 22.57 18.63 0.45 30.68 20.29 0.48

138 15.90 12.15 0.22 22.65 18.69 0.45 30.68 20.29 0.48

141 15.90 12.15 0.22 22.66 18.70 0.45 30.69 20.30 0.48

144 16.03 12.25 0.22 22.69 18.73 0.45 30.70 20.30 0.48

147 16.03 12.25 0.22 22.72 18.75 0.45 30.72 20.32 0.48

150 16.08 12.29 0.22 22.74 18.78 0.45 30.75 20.34 0.48
26

Figure 5. Summary graphs of undiscovered economic oil resources in (A) the entire North Slope study area and 

(B) the North Slope study area excluding the 1002 Area of the Arctic National Wildlife Refuge. Each red curve 

relates the market price (in 2007 U.S. dollars) to the estimated volume of economic resources where gas is valued 

at two-thirds the value of oil and the present value of gas accumulations is discounted for a 10-year delay; the 

green dashed vertical bars represent the volumes of technically recoverable oil, providing upper limits to the 

volume of economically recoverable oil. Thus, for the entire North Slope study area (A), at a market price of $72 per 

barrel (orange dashed horizontal line), at the 95th-fractile resource estimate representing a 95 percent occurrence 

probability of at least 17.4 billion barrels of oil (BBO), 14.5 BBO is economic. Similarly, at the 5th-fractile estimate 

representing a 5 percent occurrence probability of at least 32.4 BBO, 28.8 BBO is economic; at the mean estimate 

of 24.3 BBO, 21.0 BBO is economic. 
27

The 1002 Area of the Arctic National Wildlife Refuge has been closed for any type of oil and 

gas activity for decades, although it is the only part of the refuge that was given special status whereby 

the prohibition of oil and gas exploration could be removed. Recognizing the longstanding prohibition 

on oil and gas activities, the estimates for economic oil shown in table 5 did not incorporate the 

resources assigned to the 1002 Area. At $72 per barrel, economic oil volumes at the 95th-fractile, the 

mean, and the 5th-fractile resource estimates are predicted to be 9.0 BBO, 11.3 BBO, and 14.2 BBO, 

respectively. Alternatively, at $42 per barrel, the economic oil volumes at the 95th-fractile, the mean, 

and the 5th-fractile estimates are predicted to be 4.0 BBO, 5.9 BBO, and 7.7 BBO, respectively, and at 

$108 per barrel, corresponding estimates of economic oil are 10.0 BBO, 12.3 BBO, and 15.6 BBO, 

respectively. Figure 5B shows the data displayed in table 5 graphically. 

At $42 per barrel, from 35 to 45 percent of the technically recoverable oil (see table 1) in areas 

outside the 1002 Area is economic while 80 to 90 percent of the oil in the 1002 Area is economic. 

According to table 5, for areas outside of the 1002 Area, the lowest price at which it is economic to 

initiate exploration is about $30 per barrel at the mean and 5th-fractile estimates. The threshold price to 

initiate exploration in the 1002 Area is around $21 and $20 per barrel for undiscovered resources 

represented by the mean and 5th-fractile estimates, respectively. 

Estimated Economic Gas in Undiscovered Gas Accumulations

Table 6 and figure 6 show estimates of the undiscovered economically recoverable gas in 

nonassociated gas accumulations assuming a 10-year and also a 20-year delay between disbursement of 

exploration expenditures and project startup. These scenarios model the current situation where 

construction of a major gas pipeline from the North Slope is not expected for 10 years. After the 

pipeline is operational, proven gas reserves at Prudhoe Bay could fill the pipeline for another 10 years, 

implying a 20-year delay. At $8/MCF (equivalent to $72/barrel oil market price) the economic 

nonassociated gas resources at the 95th-fractile, mean, and 5th-fractile estimates are predicted to be 10.8 

TCF, 16.8 TCF, and 31.9 TCF, respectively. At the equivalent of a $42/barrel oil price, $4.67/MCF, it is 

not economic to explore for and develop undiscovered gas accumulations. At $12/MCF ($108/barrel), 

the economic nonassociated gas resources at the 95th-fractile, mean, and 5th-fractile estimates in gas 

accumulations are 40.7 TCF, 62.4 TCF, and 91.1 TCF, respectively. At $8/MCF, a 20-year delay 

reduces the economic nonassociated gas at the mean estimate to 14.4 TCF from 16.8 TCF (a 15 percent 

reduction). At $12/MCF, a 20-year delay reduces economic gas at the mean estimate to 45.3 TCF from 

62.4 TCF (a 27 percent reduction). The results illustrate how uncertainties in access to pipeline capacity 

for new discoveries produce incentives to delay exploration expenditures. Furthermore, uncertainty in 

the sizes of the potential economic resources, in turn, directly affects the size of the pipeline to be built. 

At the mean estimate, the 1002 Area of ANWR accounted for 43 percent of the undiscovered 

crude oil in the North Slope study area, but the 1002 Area accounts for less than 4 percent of the North 

Slope study area’s nonassociated gas. The geologic underpinnings of these estimates are provided in 

detail in the U.S. Geological Survey 1998 assessment (Bird, 1999). If this gas assessment is correct, 

then the effects of prohibiting exploration on total economic gas would be small if the 1002 Area were 

removed from table 6. 

Table 6 also shows the volumes of natural gas liquids (NGL) that could be recovered during 

production of nonassociated gas. Although the fractions of NGL are modest compared to economic 

crude oil resources at comparable prices, revenues from NGL production will enhance the economics of 

nonassociated gas projects.
28

Table 5. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the North Slope study area excluding resources in the 1002 Area of the Arctic National Wildlife 

Refuge, available as a function of specified market prices that offset costs of finding, developing, producing, and 

transporting the oil to market. 

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of undiscovered oil accumulations based on the North 

Slope study area aggregation except the 1002 Area has been excluded. Results of computations shown in the table are based 

on the assumption that sales of gas in gas discoveries are delayed 10 years. Prices are in 2007 dollars. Asc. gas, associated 

gas; $/bbl, dollars per barrel; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; BBL, billions of barrels of 

natural gas liquids]

Oil 

price

($/bbl)

95th-fractile estimate Mean estimate 5th-fractile estimate

Oil

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

Oil

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

Oil

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

27.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

30.00 0.00 0.00 0.00 0.66 0.75 0.01 0.88 0.64 0.01

33.00 1.70 1.92 0.03 2.40 2.67 0.05 3.08 2.38 0.03 

36.00 2.30 2.58 0.05 3.05 3.42 0.06 3.91 3.14 0.05

39.00 2.80 3.15 0.06 4.17 4.70 0.09 5.65 4.64 0.08

42.00 4.00 4.23 0.07 5.87 6.66 0.12 7.69 6.46 0.10

45.00 5.15 5.18 0.08 6.90 7.80 0.14 9.61 8.26 0.14

48.00 6.41 6.19 0.08 8.06 9.08 0.17 10.47 9.09 0.15

51.00 6.69 6.48 0.09 8.62 9.71 0.18 11.32 9.94 0.17

54.00 7.13 6.82 0.09 9.39 10.59 0.20 11.95 10.49 0.18

57.00 7.70 7.33 0.10 9.82 11.08 0.21 12.52 11.01 0.19

60.00 7.89 7.54 0.10 10.10 11.40 0.21 13.19 11.69 0.20

63.00 8.36 7.96 0.10 10.65 12.02 0.23 13.46 11.93 0.21

66.00 8.43 8.02 0.10 10.92 12.33 0.23 13.79 12.22 0.21

69.00 8.84 8.40 0.11 11.04 12.46 0.24 13.97 12.38 0.22

72.00 9.03 8.59 0.11 11.28 12.73 0.24 14.20 12.63 0.22

75.00 9.12 8.68 0.11 11.41 12.88 0.24 14.54 12.92 0.23

78.00 9.34 8.85 0.11 11.59 13.07 0.25 14.70 13.03 0.23

81.00 9.36 8.87 0.11 11.62 13.09 0.25 14.79 13.12 0.23

84.00 9.50 9.00 0.11 11.80 13.28 0.25 14.88 13.19 0.23

87.00 9.59 9.06 0.11 12.01 13.48 0.26 15.07 13.35 0.23

90.00 9.70 9.17 0.12 12.02 13.50 0.26 15.14 13.42 0.23

93.00 9.72 9.18 0.12 12.12 13.60 0.26 15.25 13.51 0.24

96.00 9.80 9.24 0.12 12.20 13.67 0.26 15.30 13.54 0.24

99.00 9.93 9.33 0.12 12.23 13.71 0.26 15.35 13.58 0.24

102.00 9.94 9.33 0.12 12.27 13.74 0.26 15.43 13.62 0.24

105.00 9.95 9.34 0.12 12.29 13.76 0.26 15.48 13.65 0.24

108.00 9.96 9.34 0.12 12.29 13.76 0.26 15.56 13.74 0.24

111.00 10.01 9.40 0.12 12.34 13.79 0.26 15.61 13.78 0.24

114.00 10.07 9.44 0.12 12.38 13.84 0.26 15.61 13.79 0.24

117.00 10.12 9.47 0.12 12.49 13.94 0.26 15.62 13.79 0.24

120.00 10.19 9.53 0.12 12.53 13.99 0.26 15.69 13.84 0.24

123.00 10.19 9.53 0.12 12.54 13.99 0.26 15.69 13.85 0.24

126.00 10.19 9.53 0.12 12.54 13.99 0.26 15.75 13.88 0.24

129.00 10.19 9.53 0.12 12.54 13.99 0.26 15.77 13.89 0.24

132.00 10.25 9.57 0.12 12.54 14.00 0.27 15.81 13.92 0.24
29

Table 5. Volumes of oil, associated gas, and natural gas liquids (NGL) from undiscovered oil accumulations, 

estimated for the North Slope study area excluding resources in the 1002 Area of the Arctic National Wildlife 

Refuge, available as a function of specified market prices that offset costs of finding, developing, producing, and 

transporting the oil to market.—Continued

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of undiscovered oil accumulations based on the North 

Slope study area aggregation except the 1002 Area has been excluded. Results of computations shown in the table are based 

on the assumption that sales of gas in gas discoveries are delayed 10 years. Prices are in 2007 dollars. Asc. gas, associated

gas; $/bbl, dollars per barrel; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; BBL, billions of barrels of 

natural gas liquids]

Oil 95th-fractile estimate Mean estimate 5th-fractile estimate

price

($/bbl)

135.00

Oil Asc. gas NGL

(BBO) (TCF) (BBL)

10.25 9.57 0.12

Oil

(BBO)

12.59

Asc. gas

(TCF)

14.04

NGL

(BBL)

0.27

Oil Asc. gas NGL

(BBO) (TCF) (BBL)

15.88 13.98 0.24

138.00 10.29 9.61 0.12 12.66 14.10 0.27 15.88 13.98 0.24

141.00 10.29 9.61 0.12 12.67 14.11 0.27 15.88 13.99 0.24

144.00 10.39 9.69 0.12 12.70 14.14 0.27 15.89 13.99 0.24

147.00 10.39 9.69 0.12 12.73 14.16 0.27 15.92 14.01 0.24

150.00 10.44 9.73 0.12 12.76 14.19 0.27 15.95 14.03 0.24
30

Table 6. Volumes of nonassociated gas and natural gas liquids (NGL) from undiscovered gas accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices that offset costs 

of finding, developing, producing, and transporting the gas to market. 

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of gas accumulations based on the North Slope study 

area aggregation consisting of all State, Federal, and Native lands in the National Petroleum Reserve in Alaska (NPRA), the 

central North Slope, the 1002 Area, and the western North Slope. Results of computations shown in the table are based on 

the assumption that sales of gas in gas discoveries are delayed 10 and 20 years. Prices are in 2007 dollars; $/bbl, dollars per 

barrel; $/MCF, dollars per thousand cubic feet; TCF, trillions of cubic feet of gas; BBL, billions of barrels of natural gas 

liquids]

Oil 

price

($/bbl)

Gas 

price

($/MCF)

95th-fractile estimate Mean estimate 5th-fractile estimate

10-year delay 20-year delay 10-year delay 20-year delay 10-year delay 20-year delay

Gas

(TCF)

NGL

(BBL)

Gas

(TCF)

NGL

(BBL)

Gas

(TCF)

NGL

(BBL)

Gas

(TCF)

NGL

(BBL)

Gas

(TCF)

NGL

(BBL)

Gas

(TCF)

NGL

(BBL)

27 3.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

30 3.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

33 3.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

36 4.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

39 4.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

42 4.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

45 5.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

48 5.33 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

51 5.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

54 6.00 0.37 0.04 0.37 0.04 0.65 0.05 0.57 0.05 0.99 0.07 0.98 0.07

57 6.33 0.66 0.05 0.66 0.05 1.70 0.08 1.08 0.07 2.71 0.09 2.70 0.09

60 6.67 1.37 0.06 1.37 0.06 3.04 0.09 2.52 0.09 5.10 0.12 5.09 0.12

63 7.00 2.00 0.07 1.91 0.07 6.14 0.13 5.58 0.13 12.70 0.20 12.68 0.20

66 7.33 6.42 0.20 5.50 0.19 9.67 0.18 9.07 0.17 17.89 0.26 17.87 0.26

69 7.67 7.28 0.21 7.30 0.21 12.03 0.21 11.41 0.21 20.12 0.28 20.10 0.28

72 8.00 10.78 0.26 10.77 0.25 16.83 0.27 14.36 0.25 31.94 0.40 23.58 0.32

75 8.33 15.59 0.31 15.57 0.31 20.67 0.32 19.96 0.31 41.06 0.51 33.59 0.43

78 8.67 18.47 0.34 17.33 0.33 26.79 0.39 22.12 0.34 47.14 0.57 35.88 0.46

81 9.00 21.47 0.37 19.66 0.35 29.01 0.42 24.31 0.36 59.12 0.69 46.83 0.57

84 9.33 26.95 0.43 23.81 0.39 38.36 0.53 26.50 0.39 64.20 0.74 52.11 0.62

87 9.67 29.45 0.46 26.28 0.42 45.17 0.61 30.29 0.44 69.83 0.79 55.53 0.66

90 10.00 30.71 0.47 26.47 0.43 45.77 0.61 36.35 0.50 74.59 0.84 62.01 0.72 

93 10.33 33.83 0.51 27.52 0.44 49.69 0.66 37.77 0.52 77.31 0.86 63.85 0.74

96 10.67 37.70 0.54 33.64 0.50 54.97 0.72 39.65 0.54 81.16 0.90 66.61 0.77

99 11.00 40.06 0.57 34.63 0.51 58.07 0.75 40.06 0.54 87.48 0.95 71.37 0.81

102 11.33 40.15 0.57 34.72 0.51 59.45 0.77 41.07 0.55 90.89 0.99 72.02 0.82

105 11.67 40.59 0.57 34.72 0.51 62.24 0.80 41.51 0.56 90.89 0.99 72.02 0.82

108 12.00 40.73 0.58 34.86 0.51 62.35 0.80 45.34 0.60 91.10 1.00 74.90 0.85

111 12.33 41.06 0.58 34.86 0.51 65.35 0.83 45.37 0.60 91.54 1.00 76.64 0.86

114 12.67 42.54 0.60 34.86 0.51 65.91 0.84 45.37 0.60 96.27 1.05 76.75 0.87

117 13.00 42.57 0.60 34.90 0.51 67.68 0.86 45.41 0.60 96.30 1.05 77.53 0.88

120 13.33 44.23 0.62 35.33 0.52 69.79 0.88 45.41 0.60 98.43 1.06 77.53 0.88

123 13.67 46.32 0.63 36.58 0.53 69.79 0.88 47.51 0.62 100.80 1.09 77.53 0.88

126 14.00 46.32 0.63 36.90 0.54 69.79 0.88 47.51 0.62 102.35 1.10 80.23 0.90

129 14.33 46.37 0.64 36.90 0.54 69.79 0.88 47.52 0.62 102.56 1.10 81.05 0.90
31

Table 6. Volumes of nonassociated gas and natural gas liquids (NGL) from undiscovered gas accumulations, 

estimated for the entire North Slope study area, available as a function of specified market prices that offset costs 

of finding, developing, producing, and transporting the gas to market.—Continued

[Volumes represent the 95th-fractile, mean, and 5th-fractile estimates of gas accumulations based on the North Slope study 

area aggregation consisting of all State, Federal, and Native lands in the National Petroleum Reserve in Alaska (NPRA), the 

central North Slope, the 1002 Area, and the western North Slope. Results of computations shown in the table are based on 

the assumption that sales of gas in gas discoveries are delayed 10 and 20 years. Prices are in 2007 dollars; $/bbl, dollars per 

barrel; $/MCF, dollars per thousand cubic feet; TCF, trillions of cubic feet of gas; BBL, billions of barrels of natural gas 

liquids]

95th-fractile estimate Mean estimate 5th-fractile estimate

Oil 

price

($/bbl)

132

Gas 

price

($/MCF)

14.67

10-year delay 20-year delay

Gas NGL Gas NGL

(TCF) (BBL) (TCF) (BBL)

46.37 0.64 38.93 0.56

10-year delay 20-year delay 

Gas NGL Gas NGL

(TCF) (BBL) (TCF) (BBL)

69.79 0.88 47.52 0.62

10-year delay 20-year delay

Gas NGL Gas NGL

(TCF) (BBL) (TCF) (BBL)

102.57 1.10 81.06 0.90

135 15.00 46.53 0.64 38.93 0.56 71.80 0.91 47.85 0.63 103.70 1.11 83.20 0.92

138 15.33 47.37 0.65 38.94 0.56 74.05 0.93 49.72 0.64 104.62 1.12 86.72 0.96

141 15.67 47.37 0.65 38.94 0.56 75.29 0.94 53.42 0.69 105.72 1.13 86.72 0.96

144 16.00 47.37 0.65 39.00 0.56 75.69 0.95 55.89 0.71 106.12 1.13 88.55 0.98

147 16.33 48.55 0.66 41.27 0.58 75.75 0.95 55.89 0.71 106.92 1.14 88.55 0.98

150 16.67 50.38 0.68 41.27 0.58 76.29 0.95 55.89 0.71 106.92 1.14 88.55 0.98
32

Figure 6. Summary graph of undiscovered economic nonassociated gas resources in the Alaska North Slope 

study area. The economic analysis assumed that gas is valued (in 2007 U.S. dollars) at two-thirds the value of oil, 

and the present value of gas was discounted for delays in pipeline availability of 10 years (blue curves) and 20 

years (red curves); the green dashed vertical bars represent volumes of technically recoverable gas, providing 

upper limits to the volume of economically recoverable gas. Thus, at a market price of $12 per thousand cubic feet 

(orange dashed horizontal line) with a 10-year delay in pipeline availability, at the 95th-fractile resource estimate 

representing a 95 percent occurrence probability of at least 74.5 trillion cubic feet (TCF) of gas, 40.7 TCF is 

economic. Similarly, at the 5th-fractile estimate representing a 5 percent occurrence probability of at least 135.0 

TCF of gas, 91.1 TCF is economic; at the mean estimate of 102.6 TCF of gas, 62.4 TCF is economic (see table 6.) 

The cost functions show that nonassociated gas is responsive to market prices between $8/MCF 

and $12/MCF. At $8/MCF, only 15 to 24 percent of the technically recoverable gas can be found, 

developed, and produced commercially. However, at $12/MCF, the percentage of the economic 

technically recoverable gas jumps from 55 to 67 percent. The 50 percent increase in price results in an 

increase in the amount of economic gas at the 95th-fractile estimate from 10.8 to 40.7 and at the 5thfractile estimate, economic gas increases from 31.9 TCF to 91.1 TCF. 

Conclusions and Limitations

The North Slope study area contains several of the largest onshore discoveries in North America. 

Results of the geologic assessment confirm that the largest oil accumulations have already been found. 

The geologic assessment predicts size frequency distributions of undiscovered oil accumulations outside 

the 1002 Area to be marginal in size (less than 500 MMBO; 3 TCF). Many of these marginally sized 

accumulations may not be economic unless they occur in clusters and can share transportation facilities. 

TAPS has been in operation for more than 30 years, and declining flow rates jeopardize its continuing 

operation. The timely exploration and development of new oil fields are particularly important to their 

commercial viability before TAPS is abandoned. In contrast to the oil resource development, natural gas 

resources have been stranded on the North Slope for decades and the timing of construction of the gas 

transportation system is uncertain. 
33

The surge and volatility in international oil prices from mid-2005 through 2008 have produced 

chaotic market conditions for the oil and gas industry service sector. Costs have escalated with price 

increases and have appeared to dampen new exploration and development. However, as prices increase, 

the unforeseen opportunities for new development technology and innovative development strategies 

will undoubtedly occur. The geologic assessments were based on historical oil and gas recovery factors 

assuming standard primary and waterflood development practices. If high oil prices are sustained into 

the future, it is expected that new technology and development strategies will lead to higher recovery 

factors. These factors would increase both the technically and economically recoverable resource 

estimates from the current assessment. 

The dampening effect of an additional 10-year delay tends to reduce payoff and results in a 

reduction of 14 to 27 percent in the amount of economic gas that can be found and discovered at market 

prices of $12/MCF. At $12/MCF, the volume associated with the reduction in the economic gas based 

on the mean estimate is significant (17.0 TCF) relative to the proven gas reserves in the area (30 to 33 

TCF). This effect on gas economics also affects the expected profitability of oil exploration where oil 

and gas accumulations are thought to occur in the same area. 

Acknowledgments 

We are grateful for the reviews of Keith Long, Ken Bird, and James Coleman of the U.S. 

Geological Survey and James Craig of the Minerals Management Service. We also would like to thank 

Elizabeth Good (USGS) for editorial assistance and Anna Glover (USGS) and Cathy Knutson (USGS) 

for graphic design support. 

References Cited 

Alaska Department of Revenue, Tax Division, 2007, Fall 2007 revenue sources book: Anchorage, 

Alaska, 126 p. (Also available online at 

http://www.tax.alaska.gov/programs/documentviewer/viewer.aspx?255.) 

Alaska Department of Revenue, Tax Division, 2008, Spring 2008 forecast: Anchorage, Alaska, 11 p., 

available online at http://www.tax.alaska.gov/programs/documentviewer/viewer.aspx?1338f.

(Accessed August 2008.) 

American Petroleum Institute, 1997–2005, Joint association survey of drilling costs: Washington, D.C., 

American Petroleum Institute, pagination varies by year.

ARCO Alaska Inc., Anadarko Petroleum Corp., and Union Texas Petroleum LLC, 1998, Alpine written 

testimony, Alpine Pool Rules Hearing, Alaska Oil and Gas Conservation Commission, December 3, 

1998: Anchorage, Alaska. 

Atkinson, Ian, Theuveny, Bertrand, Berard, Michel, Conort, Gilbert, Groves, Joel, Lowe, Trey, 

McDiarmid, Allan, Mehdizadeh, Parviz, Perciot, Patrick, Pinguet, Bruno, Smith, Gerald, and 

Williamson, K.J., 2005, A new horizon in multiphase flow measurement: Oilfield Review, v. 16, no. 

14, Winter 2004/2005, p. 52–63. (Also available online at 

http://www.slb.com/media/services/resources/oilfieldreview/ors04/win04/05_multiphase_flow.pdf.) 

Attanasi, E.D., 1998, Economics and the 1995 National Assessment of United States Oil and Gas 

Resources: U.S. Geological Survey Circular 1145, 35 p. (Also available at 

http://pubs.usgs.gov/circ/1998/c1145/c1145.html.) 
34

Attanasi, E.D., 1999, Economics of undiscovered oil in the 1002 Area of the Arctic National Wildlife 

Refuge, chap. EA of ANWR Assessment Team, The oil and gas resource potential of the Arctic 

National Wildlife Refuge 1002 Area, Alaska: U.S. Geological Survey Open-File Report 98–34, 59 p., 

on CD-ROM. (Also available online at http://pubs.usgs.gov/of/1998/ofr-98-0034/.) (Accessed 

February 27, 2009.) 

Attanasi, E.D., 2003, Economics of undiscovered oil in Federal lands on the National Petroleum 

Reserve, Alaska: U.S. Geological Survey Open-File Report 03–44, 63 p., available only online at 

http://pubs.usgs.gov/of/2003/of03-044/. (Accessed February 27, 2009.) 

Attanasi, E.D., 2005a, Undiscovered oil resources in the Federal portion of the 1002 Area of the Arctic 

National Wildlife Refuge—An economic update: U.S. Geological Survey Open-File Report 2005–

1217, 29 p., available only online at http://pubs.usgs.gov/of/2005/1217/. (Accessed February 27, 

2009.) 

Attanasi, E.D., 2005b, Economics of 1998 U.S. Geological Survey’s 1002 Area regional assessment—

An economic update: U.S. Geological Survey Open-File Report 2005–1359, 10 p., available only 

online at http://pubs.usgs.gov/of/2005/1359/. (Accessed February 27, 2009.) 

Attanasi, E.D., and Bird, K.J. [1996], Economics and undiscovered conventional oil and gas 

accumulations in the 1995 National Assessment of U.S. Oil and Gas Resources—Alaska: U.S. 

Geological Survey Open-File Report 95–75–J, 48 p., available online at 

http://pubs.er.usgs.gov/usgspubs/ofr/ofr9575J. (Accessed February 27, 2009.) 

Attanasi, E.D., and Freeman, P.A., 2005, Economics of undiscovered oil and gas in the central North 

Slope, Alaska: U.S. Geological Survey Open-File Report 2005–1276, 39 p. (Version 1.1 was released 

January 13, 2006, and is available online at http://pubs.usgs.gov/of/2005/1276/.) (Accessed February 

27, 2009.) 

Baker, R.A., Gehman, H.M., James, W.R., and White, D.A., 1984, Geologic field number and size 

assessments of oil and gas plays: American Association of Petroleum Geologists Bulletin, v. 68, no. 4, 

p. 426–432. 

Bird, K.J., 1999, Assessment overview, chap. AO of ANWR Assessment Team, The oil and gas 

resource potential of the Arctic National Wildlife Refuge 1002 Area, Alaska: U.S. Geological Survey 

Open-File Report 98–34, 56 p., on CD-ROM. (Also available online at 

http://pubs.usgs.gov/of/1998/ofr-98-0034/.) (Accessed February 27, 2009.) 

Bird, K.J., and Houseknecht, D.W., 2002, U.S. Geological Survey 2002 petroleum resource assessment 

of the National Petroleum Reserve in Alaska (NPRA): U.S. Geological Survey Fact Sheet 045–02, 6 

p., available online at http://pubs.usgs.gov/fs/2002/fs045-02/. (Accessed February 27, 2009.) 

British Petroleum Exploration (Alaska), 1996, Northstar Development Project—Conceptual 

Engineering Report, report submitted for evaluation to the Alaska Department of Natural Resources: 

Anchorage, Alaska 

ConocoPhillips, 2007, ANS natural gas pipeline—Proposal to the State of Alaska, November 30, 2007: 

[Houston,] ConocoPhillips, 115 p. (Available from the Alaska Department of Natural Resources, 

Anchorage, Alaska.) 

Corbett, K.T., Bowen, R.R., and Petersen, C.W., 2003, High strength steel pipeline economics, in v. 4 of

Ayer, Raghavan, Langen, Ivar, Knapp, R.H., and Chung, J.S., eds., Proceedings of the Thirteenth 

International Offshore and Polar Engineering Conference, 25–30th May 2003, Honolulu, Hawaii: 

Cupertino, Calif., International Society of Offshore and Polar Engineers, p. 105–112. 

Craig, J.D., 2002, Economic analysis of the development alternatives for the Liberty prospect, Beaufort 

Sea, Alaska, app. D–1 in v. IV, Appendices, of Liberty development and production plan; Final 

environmental impact statement: Minerals Management Service [Report] OCS EIS/EA 2002–019, p. 
35

D1–1 to D1–22, available online at 

http://www.mms.gov/alaska/ref/EIS%20EA/libertyfeis/Documents/Liberty%20FEIS%20Vol%204.pdf. 

(Accessed April 8, 2009.) 

Energy Information Administration, 2008, Annual energy outlook 2008, with projections to 2030: 

Energy Information Administration [Report] DOE/EIA–0383(2008), 215 p., available online at 

http://www.eia.doe.gov/oiaf/aeo/pdf/0383(2008).pdf. (Accessed April 8, 2009.) 

Garrity, C.P., Houseknecht, D.W., and Bird, K.J., 2002, U.S. Geological Survey 2002 petroleum 

resource assessment of the National Petroleum Reserve in Alaska (NPRA)—GIS play maps: U.S. 

Geological Survey Open-File Report 02–439, available only online at 

http://pubs.usgs.gov/of/2002/of02-439/. (Accessed February 27, 2009.) 

Garrity, C.P., Houseknecht, D.W., Bird, K.J., Potter, C.J., Moore, T.E., Nelson, P.H., and Schenk, C.J., 

2005, U.S. Geological Survey 2005 oil and gas resource assessment of the central North Slope, 

Alaska; Play maps and results: U.S. Geological Survey Open-File Report 2005–1182, 24 p., available 

online at http://pubs.usgs.gov/of/2005/1182/. (Accessed February 27, 2009.) 

Gingrich, Dean, Knock, Doug, and Masters, Ron, 2001, Geophysical interpretation methods applied at 

Alpine oil field, North Slope Alaska: The Leading Edge, v. 20, no. 7 (July), p. 730–738. 

Houseknecht, D.W., and Bird, K.J., 2006, Oil and gas resources of the Arctic Alaska Petroleum 

Province, chap. A of Haeussler, P.J., and Galloway, J.P., eds., Studies by the U.S. Geological Survey 

in Alaska, 2005: U.S. Geological Survey Professional Paper 1732, p. 1–11, available only online at 

http://pubs.usgs.gov/pp/pp1732/pp1732a/index.html. (Accessed February 27, 2009.) 

IHS Inc., 2007, QUE$TOR petroleum field development and production cost database, v. 9.5: 

Englewood, Colo., IHS Inc.

Joshi, S.D., 1991a, Drainage areas and well spacing, in Fritz, R.D., Horn, M.K., and Joshi, S.D., eds., 

Geological aspects of horizontal drilling: American Association of Petroleum Geologists Continuing 

Education Course Note Series 33, p. 65–78. 

Joshi, S.D., 1991b, Factor influencing productivity, in Fritz, R.D., Horn, M.K., and Joshi, S.D., eds., 

Geological aspects of horizontal drilling: American Association of Petroleum Geologists Continuing 

Education Course Note Series 33, p. 80–90. 

Kaltenbach, Bob, Walsh, Chantal, Foerster, Cathy, Walsh, Tom, MacDonald, Jan, Stokes, Pete, Livesey, 

Chris, and Nebesky, Will, 2004, North Slope of Alaska facility sharing study, prepared for Division of 

Oil and Gas, Alaska Department of Natural Resources, by Petrotechnical Resources of Alaska: 62 p., 

available online at 

http://www.dog.dnr.state.ak.us/oil/products/publications/otherreports/nsfacility/share.htm. (Accessed 

February 27, 2009.) 

Kuuskraa, V.A., Morra, F., Jr., and Godec, M.L., 1987, Importance of cost/price relationships for leastcost oil and gas resources, in Proceedings of 1987 Hydrocarbon Economics and Evaluation 

Symposium, Dallas, Texas: Richardson, Tex., Society of Petroleum Engineers, SPE Paper 16290, p. 

25–42. 

National Petroleum Council, 1981a, U.S. Arctic oil and gas: Washington D.C., National Petroleum 

Council, December 1981, 286 p. 

National Petroleum Council, 1981b, Working papers of the Production Task Group of the National 

Petroleum Council's Committee on Arctic Oil and Gas Resources: Washington, D.C., National 

Petroleum Council, 372 p. 

National Petroleum Council, 2003, Balancing natural gas policy—Fueling the demands of a growing 

economy, v. IV, Supply Task Force Report: Washington, D.C., National Petroleum Council, 456 p. 
36

Nehring Associates, Inc., 2004, Significant oil and gas fields of the United States database: Colorado 

Springs, Colo., Nehring Associates, Inc. 

Nelson, Kristen, 2004, Alternatives to Alpine satellite project proposed: Anchorage, Alaska, Petroleum 

News, January 28, 2004, p. 1, 12–13. 

Redman, R.S., 2002, Horizontal miscible water alternating gas development of the Alpine field, Alaska, 

in Society of Petroleum Engineers Western Regional/AAPG Pacific Section Joint Meeting, 20–22nd 

May 2002, Anchorage, Alaska: Richardson, Tex., Society of Petroleum Engineers, SPE Paper 76819, 

8 p. 

Schuenemeyer, J.H., 1999, Methodology, chap. ME of ANWR Assessment Team, The oil and gas 

resource potential of the Arctic National Wildlife Refuge 1002 Area, Alaska: U.S. Geological Survey 

Open-File Report 98–34, 28 p., on CD-ROM. (Also available online at 

http://pubs.usgs.gov/of/1998/ofr-98-0034/.) (Accessed February 27, 2009.) 

Schuenemeyer, J.H., 2003, Methodology and results for the assessment of oil and gas resources, 

National Petroleum Reserve, Alaska: U.S. Geological Survey Open-File Report 03–118, 201 p., 

available online at http://geopubs.wr.usgs.gov/open-file/of03-118/. (Accessed February 27, 2009.) 

Schuenemeyer, J.H., 2005, Methodology for the 2005 USGS assessment of undiscovered oil and gas 

resources, central North Slope, Alaska: U.S. Geological Survey Open-File Report 2005–1410, 82 p., 

available online at http://pubs.usgs.gov/of/2005/1410/. (Accessed February 27, 2009.) 

Thomas, C.P., Doughty, T.C., Faulder, D.D., Harrision, W.E., Irving, J.S., Jamison, H.C., and White, 

G.J., 1991, Alaska oil and gas energy wealth or vanishing opportunity: Idaho Falls, Idaho, E.G. and G, 

Idaho, Inc., DOE/ID/01570-H1, 279 p. 

Thomas, C.P., Faulder, D.D., Doughty, T.C., Hite, D.M., and White, G.J., 2007, Alaska North Slope oil 

and gas—A promising future or an area in decline? (full report): National Energy Technology 

Laboratory [Report] DOE/ NETL-2007/1279, 479 p., available online at 

http://www.netl.doe.gov/technologies/oilgas/publications/EPreports/ANSFullReportFinalAugust2007.pdf. (Accessed April 9, 2009.) 

TransCanada, 2007, Application for license—Alaska Gasline Inducement Act, Public application and 

appendices: Calgary, Alberta, Canada, TransCanada Pipelines Limited, available online at 

http://www.gov.state.ak.us/agia/. (Accessed September 30, 2008.) 

Vidas, E.H., Hugman, R.H., and Haverkamp, D.S., 1993, Guide to the hydrocarbon supply model—

1993 update: Arlington, Va., Energy and Environmental Analysis, Inc., prepared for the Gas Research 

Institute, 272 p. 

Young, J.H., and Hauser, W.S., 1986, Economics of oil and gas production from the Arctic Refuge 

(ANWR): Anchorage, Alaska, U.S. Bureau of Land Management, Alaska State Office, 101 p. 
37

Appendix 1. Volumes Associated with the Mean Estimate for Each Play in Each 

of the Four Assessment Areas

Tables A1-1 through A1-4 provide the volumes of undiscovered oil and gas resources associated 

with the mean estimates of each play assessed in the National Petroleum Reserve in Alaska (NPRA), the 

central North Slope, the 1002 Area of the Arctic National Wildlife Refuge and the western North Slope 

subareas (see text fig. 1). The original assessment data from the earlier assessments of the 1002 Area 

(Bird, 1999), the NPRA (Bird and Houseknecht, 2002), and the central North Slope (Garrity and others, 

2005) were adjusted by the assessment geologists to reflect a common minimum size accumulation with 

separate distributions for numbers of oil and gas prospects. These data were probabilistically aggregated 

along with the assessment results for the western North Slope to arrive at the volumes shown in table 1 

of the text (written communications, J.H. Schuenemeyer, Southwest Statistical Consulting, November 

2007). Text figures 2A and 2B show the aggregate accumulation frequency size distributions associated 

with the 95th- and 5th-fractile estimates as well as the mean value estimates. 
38

Table A1–1. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by 

play for the National Petroleum Reserve in Alaska.

[Asc. gas, associated gas; Nonasc. gas, nonassociated gas; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; 

BBL, billions of barrels of natural gas liquids (NGL); -- (dashes), volume smaller than the minimum assessed accumulation 

size] 

Oil accumulations Gas accumulations

Play Oil 

(BBO)

Asc. gas NGL

(TCF) (BBL)

Nonasc. NGL

gas (BBL) (TCF)

Brookian Topset

Brookian Clinoform North

Brookian Clinoform Central

Brookian Clinoform South-Shallow

Brookian Clinoform South-Deep

Beaufortian Cretaceous Topset North

Beaufortian Cretaceous Topset South

Beaufortian Upper Jurassic Topset NE

Beaufortian Upper Jurassic Topset SE

Beaufortian Upper Jurassic Topset NW

Beaufortian Upper Jurassic Topset SW

Beaufortian Lower Jurassic Topset

Beaufortian Clinoform

Brookian Topset Structural

Torok Structural

Ellesmerian Structural

Ellesmerian Thrust Belt

Ellesmerian-Ivishak

Ellesmerian Echooka North

Ellesmerian Echooka South

Ellesmerian Lisburne North

Ellesmerian Lisburne South

Ellesmerian Endicott North

Ellesmerian Endicott South

 Total

0.22

1.28

1.04

0.49

--

0.11

--

4.96

0.00

1.93

--

0.09

0.01

0.14

0.03

0.00

0.01

0.10

0.01

--

0.03

--

0.00

--

0.19

1.09

1.32

0.35

--

0.09

--

6.05

0.00

2.34

--

0.05

0.00

0.00

0.02

0.00

0.01

0.06

0.01

--

0.02

--

0.00

--

0.00

0.01

0.03

0.00

--

0.00

--

0.11

0.00

0.04

--

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

--

0.00

--

0.00

--

0.19

0.67

5.48

2.33

3.98

0.42

2.20

--

5.30

--

5.43

0.79

0.80

11.00

18.83

2.06

1.48

0.11

0.01

0.50

0.02

0.65

--

1.08

0.00

0.01

0.07

0.03

0.05

0.00

0.03

--

0.07

--

0.07

0.01

0.01

0.09

0.17

0.03

0.02

0.00

0.00

0.01

0.00

0.01

--

0.01

10.47 11.59 0.21 63.34 0.68
39

Table A1–2. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by 

play for the central North Slope.

[Asc. gas; associated gas; Nonasc. gas, nonassociated gas; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; 

BBL, billions of barrels of natural gas liquids (NGL); -- (dashes), volume smaller than the minimum assessed accumulation 

size] 

Oil accumulations Gas accumulations

Play Oil 

(BBO)

Asc. gas

(TCF)

NGL

(BBL)

Nonasc. NGL

gas (BBL) (TCF)

Brookian Clinoform

Brookian Topset

Beaufortian Upper Jurassic Topset East

Beaufortian Upper Jurassic Topset West

Beaufortian Clinoform

Beaufortian Kuparuk Topset

Beaufortian Cretaceous Shelf Margin

Triassic Barrow Arch

Ivishak Barrow Flank

Endicott

Endicott Truncation

Franklinian

Lisburne Barrow Arch

Lisburne Barrow Flank

Kemik-Thompson

Basement Involved Structural

Beaufortian Structural

Brookian Clinoform Structural South

Brookian Clinoform Structural North

Brookian Topset Structural South

Brookian Topset Structural North

Thrust Belt Triangle Zone

Thrust Belt Lisburne

Ellesmerian Structural

 Total

1.48

0.34

0.00

0.12

0.09

0.09

--

0.35

--

--

0.06

0.01

0.09

--

0.23

0.02

0.01

0.01

0.12

0.02

0.26

0.05

0.07

--

1.66

0.25

0.00

0.11

0.13

0.07

--

0.43

--

--

0.07

0.01

0.09

--

0.41

0.01

0.01

0.01

0.13

0.01

0.10

0.03

0.07

--

0.03

0.00

0.00

0.00

0.00

0.00

--

0.01

--

--

0.00

0.00

0.00

--

0.02

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

--

4.86

0.18

0.06

0.12

0.43

0.18

0.35

0.00

0.17

0.13

--

--

--

0.59

1.92

2.35

1.63

1.74

0.18

2.22

0.25

3.47

3.16

1.11

0.06

0.00

0.00

0.00

0.01

0.00

0.00

0.00

0.00

0.00

--

--

--

0.01

0.02

0.03

0.02

0.02

0.00

0.02

0.00

0.04

0.04

0.01

3.41 3.60 0.08 25.10 0.29
40

Table A1–3. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by 

play for the 1002 Area of the Arctic National Wildlife Refuge.

[Asc. gas, associated gas; Nonasc. gas, nonassociated gas; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; 

BBL, billions of barrels of natural gas liquids (NGL); -- (dashes), volume smaller than the minimum assessed accumulation 

size] 

Oil accumulations Gas accumulations

Nonasc. Play Oil Asc. gas NGL NGL

gas (BBO) (TCF) (BBL) (BBL) (TCF)

Topset 6.18 1.70 0.01 -- --

Tubidite 1.59 1.39 0.08 -- --

Wedge 0.50 0.26 0.01 -- --

Thompson 0.36 0.46 0.04 0.23 0.02

Kemik 0.05 0.06 0.01 0.06 0.00

Undeformed Franklinian 0.10 0.18 0.02 0.18 0.02

Thin-Skinned Thrust Belt 1.15 0.32 0.00 1.45 0.02

Ellesmerian Thrust Belt -- -- -- 0.87 0.02

Deformed Franklinian 0.05 0.04 0.00 0.82 0.04

Niquanak/Aurora 0.36 0.34 0.02 0.21 0.01

 Total 10.35 4.76 0.19 3.81 0.13

Table A1–4. Mean estimates of undiscovered technically recoverable volumes of conventional oil and gas by 

play for the western North Slope.

[Asc. gas, associated gas; Nonasc. gas, nonassociated gas; BBO, billions of barrels of oil; TCF, trillions of cubic feet of gas; 

BBL, billions of barrels of natural gas liquids (NGL); -- (dashes), volume smaller than the minimum assessed accumulation 

size] 

Oil accumulations

Play Oil Asc. gas

(BBO) (TCF)

Brookian Clinoform -- --

Gas accumulations

Nonasc. NGL NGL

gas (BBL) (BBL) (TCF)

-- 1.4312 0.0174

Brookian Topset 0.0059 0.0035 0.0000 0.4294 0.0035

Nanushuk Structural 0.0233 0.0105 0.0001 2.0571 0.012

Southwest Foothills Structural

 Total

0.0466

0.0758

0.0323

0.0463

0.0006

0.0007

6.4434

10.3611

0.0823

0.1152
41

Appendix 2. Allocation of Play Resources to Economic Zones

The procedure for the allocation of play resources to economic zones begins with the published 

play boundaries for the central North Slope (Garrity and others, 2005), the National Petroleum Reserve 

in Alaska (NPRA) (Garrity and others, 2003), and the 1002 Area of the Arctic National Wildlife Refuge 

(ANWR) (Bird, 1999). The western North Slope subarea constituted a single economic zone. For some 

plays, the geologists provided supplemental information that enabled subdivision of plays between oilprone and gas-prone areas. The economic zones encompassed onshore Native, Federal, and State lands 

and offshore State areas. Text figure 4 shows the individual economic zones. The economic zones 

are of a size that development hubs could evolve in each. The allocations of total play volumes by 

primary product (oil and nonassociated gas resources) were expressed as percentages. The same 

percentages were used to allocate resources at the 95th-fractile, the mean, and the 5th-fractile estimates. 

For an individual play, accumulation size class allocations were the same percentages as the primary 

product volume allocations. However, inasmuch as each economic zone has a different mix of plays, the 

size frequency distribution for undiscovered accumulations will be different across zones of the same 

study subarea. 

The NPRA was divided into eight economic zones, and 24 plays were assessed. The assessors 

posited that oil accumulations were more likely to occur in the northern and eastern parts of the NPRA 

and that the southern and western parts of the NPRA would be more prospective for natural gas 

accumulations. Table A2-1 shows the percentage of total oil resources and the percentage of 

nonassociated natural gas resources allocated to each of the eight economic zones.

There were 24 plays delineated by the geologists for the central North Slope study subarea, 

which has 3 economic zones. Geologists posited that the northern portion of the area is oil prone and the 

southern portion is gas prone. Table A2-2 shows the percentage allocations of oil and gas for plays for 

this study subarea. 

There were 10 plays delineated by geologists for the 1002 Area of the Arctic National Wildlife 

Refuge (ANWR), which has 2 economic zones (table A2-3). Plays in the western economic zone are 

characterized by a larger field size and are more oil prone than the plays in the eastern economic zone.

The western North Slope represented a single economic zone, and so the four plays delineated 

by the assessment geologists (see table A1-4) were not subdivided. The undiscovered accumulations 

assessed in the western North Slope were predominantly gas. 
42

Table A2–1. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

National Petroleum Reserve in Alaska to economic zones N110, N120, N130, N210, N220, N230, N320, and N330, 

as identified in text figure 4.

Play N110 N120 N130 N210 N220 N230 N320 N330

Oil in oil accumulations

Brookian Topset

Brookian Clinoform North

Brookian Clinoform Central

Brookian Clinoform South-Shallow

Brookian Clinoform South-Deep

Beaufortian Cretaceous Topset North

Beaufortian Cretaceous Topset South

Beaufortian Upper Jurassic Topset Northeast

Beaufortian Upper Jurassic Topset Southeast

Beaufortian Upper Jurassic Topset Northwest

Beaufortian Upper Jurassic Topset Southwest

Beaufortian Lower Jurassic Topset

Beaufortian Clinoform

Brookian Topset Structural

Torok Structural

Ellesmerian Structural

Thrust Belt

Ellesmerian Ivishak

Ellesmerian Echooka North

Ellesmerian Echooka South

Ellesmerian Lisburne North

Ellesmerian Lisburne South

Ellesmerian Endicott North

Ellesmerian Endicott South

22

49

4 

0 

0

44

0 

58

0

0

0 

10

100

2

1 

0 

0

45

79

0 

75

0

60

0 

23

40

20

0 

0

42

0 

40

0

20

0 

55

0 

12

3 

0 

0

32

15

0 

25

0

40

0 

20

10

17

0 

0

12

0 

0 

0

80

0 

35

0 

17

7 

0 

0

20

6 

0 

0

0

0 

0 

15

1

36

20

0

2

0 

2 

0

0

0 

0 

0 

17

14

0 

0

1

0 

0 

0

0

0 

0 

10

0

20

54

0

0

0 

0 

0

0

0 

0 

0 

27

28

0 

0

1

0 

0 

0

0

0 

0 

10

0

3 

23

0

0

0 

0 

0

0

0 

0 

0 

23

45

0 

0

1

0 

0 

0

0

0 

0 

0 

0

0 

1 

0

0

0 

0 

0

0

0 

0 

0 

1

1 

0 

25

0

0 

0 

0

0

0 

0 

0 

0

0 

2 

0

0

0 

0 

0

0

0 

0 

0 

1

1 

0 

75

0

0 

0 

0

0

0 

0 
43

Table A2–1. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

National Petroleum Reserve in Alaska to economic zones N110, N120, N130, N210, N220, N230, N320, and N330, 

as identified in text figure 4.—Continued

Play N110 N120 N130 N210 N220 N230 N320 N330

Gas in gas accumulations

Brookian Topset

Brookian Clinoform North

Brookian Clinoform Central

Brookian Clinoform South-Shallow

Brookian Clinoform South-Deep

Beaufortian Cretaceous Topset North

Beaufortian Cretaceous Topset South

Beaufortian Upper Jurassic Topset Northeast

Beaufortian Upper Jurassic Topset Southeast

Beaufortian Upper Jurassic Topset Northwest

Beaufortian Upper Jurassic Topset Southwest

Beaufortian Lower Jurassic Topset

Beaufortian Clinoform

Brookian Topset Structural

Torok Structural

Ellesmerian Structural

Thrust Belt

Ellesmerian Ivishak

Ellesmerian Echooka North

Ellesmerian Echooka South 

Ellesmerian Lisburne North

Ellesmerian Lisburne South

Ellesmerian Endicott North

Ellesmerian Endicott South

7

24

2 

0 

0 

33

0 

0 

3

0

0 

0 

100

2

1 

0 

0 

45

79

0 

75

0

60

20

13

45

15

0 

0 

40

8 

0 

15

0

5 

25

0

12

3 

0 

0 

32

15

15

25

20

40

20

19

30

40

0 

0 

20

35

0 

0

0

60

45

0

17

7 

0 

0 

20

6 

40

0

30

0 

20

12

1

13

7 

7 

7

15

0 

35

0

0 

0 

0

17

12

12

0 

1

0 

25

0

25

0 

20

21

0

15

30

30

0

30

0 

47

0

15

10

0

27

24

25

0 

1

0 

10

0

20

0 

15

28

0

15

60

60

0

12

0 

0

0

20

20

0

23

40

50

0 

1

0 

10

0

5

0 

5 

0

0

0 

1 

1 

0

0 

0 

0

0

0 

0 

0

1

4 

4 

25

0

0 

0 

0

0

0 

0 

0

0

0 

2 

2 

0

0 

0 

0

0

0 

0 

0

1

9 

9 

75

0

0 

0 

0

0

0 

0 
44

Table A2–2. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

central North Slope to economic zones C110, C120, and C130, as identified in text figure 4.

Play

Oil in oil 

accumulations

Gas in gas 

accumulations

C110 C120 C130 C110 C120 C130

Brookian Clinoform 53 48 0 0 56 44

Brookian Topset 46 54 0 0 62 38

Beaufortian Upper Jurassic Topset East 5 95 0 0 100 0

Beaufortian Upper Jurassic Topset West 91 9 0 0 100 0

Beaufortian Clinoform 45 56 0 0 100 0

Beaufortian Kuparuk Topset 71 29 0 0 100 0 

Beaufortian Cretaceous Shelf Margin 0 100 0 0 100 0

Triassic Barrow Arch 100 0 0 100 0 0

Ivishak Barrow Flank 6 94 0 6 94 0

Endicott 39 61 0 39 61 0 

Endicott Truncation 100 0 0 100 0 0 

Franklinian 100 0 0 100 0 0

Lisburne Barrow Arch 73 27 0 73 27 0

Lisburne Barrow Flank 3 97 0 3 97 0 

Kemik-Thompson 60 40 0 0 100 0

Basement Involved Structural 0 72 29 0 72 29

Beaufortian Structural 0 82 18 0 82 18

Brookian Clinoform Structural South 0 79 21 0 79 21

Brookian Clinoform Structural North 0 100 0 0 100 0

Brookian Topset Structural South 0 72 28 0 72 28

Brookian Topset Structural North 0 100 0 0 100 0

Thrust Belt Triangle Zone 0 9 91 0 9 91

Thrust Belt Lisburne 0 0 100 0 0 100

Ellesmerian Structural 0 47 53 0 47 53

Table A2–3. Percentage allocations of oil in oil accumulations and gas in gas accumulations for plays of the 

1002 Area of the Arctic National Wildlife Refuge to economic zones A110 and A120, as identified in text figure 4.

Play

Topset

Oil in oil 

accumulations

A110 A120

86 14

Gas in gas 

accumulations

A110 A120

0 0

Turbidite 95 5 0 0

Wedge 100 0 100 0 

Thompson 100 0 100 0

Kemik 100 0 100 0

Undeformed Franklinian 100 0 100 0

Thin-Skinned Thrust Belt 25 75 25 75

Ellesmerian Thrust Belt 0 0 10 90

Deformed Franklinian 90 10 90 10

Niguanak/Aurora 0 100 0 100
45

Appendix 3. Documentation of Cost Estimates 

Transportation Costs 

The text discussion explains the rationale for the assumptions relating to the dominant cost 

transportation component, that is, the cost component from North Slope collection points, either Pump 

Station 1 or the proposed gas conditioning plant, to the respective market. To review, the assumed 

Trans-Alaska Pipeline System (TAPS) tariff is $4.87 per barrel from Pump Station 1 to Valdez. In 

addition to this cost, there is a cost of $1.61 per barrel to transport oil from Valdez to the market. There 

is an estimated cost of $4.42 per thousand cubic feet ($4.42/MCF) for natural gas conditioning and 

pipeline shipment to the U.S. Midwest market. 

The assessment results implied that likely discovery sizes are expected to be modest by Arctic 

standards (less than 500 MMBO and 3 TCF). At the mean estimate, the technically recoverable 

resources are expected to be contained in 179 oil and 145 nonassociated gas accumulations. The 

economic zones provide a basis for transportation cost sharing of overland pipelines from the economic 

zone to TAPS or the proposed gas conditioning plant. Tables A2-1, A2-2, and A2-3 list the play 

allocations of oil and nonassociated gas accumulations to the economic zones within each North Slope 

subarea. Individual discoveries are required to bear the full cost of construction and operation of the 

feeder pipeline from the field to the overland regional pipeline. These pipeline costs are recovered by a 

tariff charged by the feeder pipeline owner. Both feeder and regional pipelines are operated as common 

carriers.

Feeder and Regional Pipeline Assumptions 

A hypothetical transportation system moves oil and gas to the central North Slope subarea where 

TAPS and a proposed natural gas conditioning plant are located. This system consists of feeder lines 

from the fields to a regional pipeline. For each discovery size class, the peak or plateau annual 

production volume was computed for the representative oil and gas discovery. The required diameter for 

the feeder lines from individual discoveries to the regional pipeline was calculated to accommodate the 

peak or plateau flow rates. The investment costs of the individual feeder lines depend on the pipeline’s 

diameter and length, that is, the average distance from the field to a regional pipeline. The tariff19 or 

charge for transporting the oil from the outlying discovery to a regional pipeline hub was computed as if 

the feeder pipeline were operated as a regulated common carrier and permitted a 12 percent after-tax 

rate of return on investment cost. The calculated tariff includes the after-tax rate of return, operating 

costs, taxes, and recovery of the initial investment during the nominal life of the field.

The size of the crude oil or gas product pipeline from the field to the regional pipeline was 

calculated such that its capacity (regulated by its diameter) would be sufficient to move the discovery’s 

peak annual plateau production to the regional line. The oil and conventional gas pipeline cost data were 

generated with the QUE$TOR software (IHS Inc., 2007). The investment costs were estimated and 

expressed in dollars per inch-diameter per mile. The costs include the installed pipe, the right of way, 

and the initial pump system. The base cost is $163,000 per inch-diameter per mile for crude oil and 

$175,000 per inch-diameter per mile for a conventional gas line. 

Base costs were scaled up to include all pipelines bundled together and installed in the overland 

pipeline corridor. To estimate costs of these additions for all feeder lines and in some cases for the 

 19The term “tariff,” as used in this report, is the charge by a publicly regulated entity; in this case a regulated common 

carrier. 
46

regional oil pipelines, diameters were increased to account for the additional bundling of utility lines 

and seawater lines (for waterflood of oil discoveries)20 to the operating field. These lines may use the 

same vertical support members and right of way as the pipeline transporting produced oil and gas to the 

regional pipeline. To account for this extra cost, the initial investment cost per inch-diameter per mile 

was increased by 100 percent for oil accumulations requiring import of injection water and 50 percent 

per inch-diameter per mile for gas discoveries. 

Booster pump stations were added to the oil and natural gas pipelines at intervals of 100 miles 

from the source. Data from studies prepared with the QUE$TOR software (IHS Inc., 2007) indicated 

that the booster pump station investment cost was equivalent to about 10 percent of the investment costs 

required for each 100 miles of pipeline length.

The sizing (diameter) for the regional oil and gas pipelines was based on the total assessed 

resources allocated to each economic zone. The regional pipeline sizing rule was conservative to allow 

for differences in the timing of discoveries, development rates, and production rates of different fields in 

the zone. Typically, the maximum pipeline capacity allows only 3 percent of the total assessed resource 

in the economic unit to be transported in a single year. If greater volumes of oil and gas resources are 

found and developed, then higher volume regional lines could be installed, and this installation would 

probably result in a slightly reduced regional pipeline tariff. 

Regional gas pipelines from the economic zone to the future gas conditioning plant near Pump 

Station 1 are typically more than 50 miles long, and it is assumed that these pipelines would be highpressure pipelines that could transport both gas and natural gas liquids in a dense phase (Corbett and 

others, 2003). The gas feeder lines from the field to the hub of the economic zone were assumed to be 

low-pressure lines, as these will be much shorter than the regional lines and require less capacity. 

Because the geologic assessment indicated that nonassociated gas accumulations are expected to be 

relatively lean, in terms of entrained liquids, it was assumed that the feeder lines transported both gas 

and minor amounts of NGL to the high-pressure regional pipelines. The procedures for computing the 

tariffs for the regional gas pipelines and the feeder lines from the outlying fields were similar to the 

procedures used to calculate tariffs for the crude oil pipeline. 

Annual operating costs for both oil and gas pipelines were estimated to be 2 percent of the initial 

pipeline investment including any additional booster pumping stations. Tariffs were estimated to 

recover operating costs, property taxes, State and Federal income taxes, recovery of original investment, 

and an after-tax rate of return of 12 percent. 

Table A3-1 shows the feeder and regional pipeline specifications assumed for each of the 

economic zones. The economic zones shown in table A3-1 correspond to the economic zones in text 

figure 4. The western North Slope was considered a single zone. Gas would be shipped east to the 

commercial gas pipeline.21 The NPRA is divided into eight economic zones. Geologists posited that oil 

accumulations were more likely to occur in the northern and eastern areas of the NPRA and that the 

southern and western areas would be more prospective for natural gas accumulations. The volume of oil 

assessed in the southernmost economic zones labeled N320 and N330 is so small that a regional oil 

pipeline was not considered. 

 20Waterflood is used in pressure maintenance and to force oil to the production well in oil accumulations. In the North 

Slope, seawater has been used for this purpose. Nearly all of the assessed undiscovered oil accumulations were in plays 

located in the northern part of the North Slope, reasonably close to the coast. 21The assessed oil is small and, if found, could probably be shipped to the port area where the Red Dog mine concentrate is 

shipped, some 200 miles from the western North Slope subarea. 
47

Table A3–1. Hypothetical pipeline system configuration distances and regional pipeline capacity by economic 

zone as identified in text figure 4.

[MMBO/D, millions of barrels of oil per day; BCF/D, billions of cubic feet of gas per day]

Regional Length of Length of pipeline Economic feeder regional Commodity capacity zone pipeline pipeline (MMBO/D or (miles) (miles) BCF/D)

1002 Area of the Arctic National Wildlife Refuge

A110 oil 12 89 0.50

gas 12 89 0.40

A120 oil 16 0 0.25

gas 16 187 0.15

Central North Slope

C110 oil 9 (

1

) (

1

) 

gas 25 (

1

) (

1

)

C120 oil 15 35 0.18

gas 15 59 1.00

C130 oil 80 (

1

) (

1

) 

gas 20 136 1.00

National Petroleum Reserve in Alaska

N110 oil 10 96 0.25

gas 10 102 0.50

N120 oil 8 167 0.25

gas 8 170 0.75

N130 oil 17 235 0.25

gas 17 236 1.00

N210 oil 12.5 107 0.09

gas 12.5 114 1.00

N220 oil 17.5 173 0.06

gas 17.5 174 1.00

N230 oil 17.5 266 0.03

gas 17.5 268 1.00

N320 oil 200 (

1

) (

1

) 

gas 5 218 0.14

N330 oil 300 0 0.00

gas 17.5 282 0.42

Western North Slope

W110 oil 200 (

1

) (

1

) 

gas 20 340 0.75

1 Because of small oil volumes, only feeder lines were hypothesized for transportation to a transshipment point, either Pump 

Station 1 of the Trans-Alaska Pipeline System or the planned gas conditioning plant.
48

For the central North Slope, the northernmost economic zone (C110) would need only oil or gas 

feeder lines because of proximity to Pump Station 1 and the proposed natural gas conditioning plant. 

For the central North Slope, the southernmost economic zone (C130) was assessed to be gas prone, and 

so no regional oil pipeline was assumed. Future oil discoveries in the middle economic zone (C120) of 

the central North Slope were assumed to tie into TAPS at a location south of Pump Station 2 (text fig. 

4). 

The 1002 Area is considered environmentally sensitive and is very compact geographically. 

Because of a need to minimize the development footprint and because of the 1002 Area’s compactness, 

the oil and gas processing facilities would be located outside the sensitive area. It is assumed that one 

leg of the regional pipeline would transport the produced fluids to the processing facilities in State or 

Native lands outside of the 1002 Federal lands. The other leg would transport the processed crude oil 

and gas to Pump Station 1 or the proposed gas conditioning plant (see fig. A3-1). 

Figure A3–1. Map showing the partition of the 1002 Area of the Arctic National Wildlife Refuge into economic 

zones (A110 and A120) and a hypothetical, generalized regional pipeline transport system from Federal portions of 

the zones to processing facility areas and then to Pump Station 1 near Prudhoe Bay. The central processing areas 

are shaded gray. The placement of pipelines shown in the figure is for purposes of cost analysis in this study and 

does not imply a suggested route for the actual system (Attanasi, 2005b).
49

Field Development Costs

Field development costs include well drilling and completion costs and the cost of facilities. The 

development cost estimates are generalized because actual field development costs will depend on sitespecific characteristics of prospects that are undefined today. In the process of developing generic cost 

functions, a number of simplifying assumptions were made to keep the economic analysis manageable. 

The simulated accumulations were first grouped into field size categories and into 5,000-foot subsurface 

depth intervals. The analysis also included the costs of vertical delineation wells for each accumulation 

evaluated. Development costs were estimated for a representative accumulation for each size and depth 

class and tested against an economic screen to determine whether the accumulations in the size and 

depth category were commercially developable.

Oil Field Design

Oil accumulation size (szo) was computed from the simulated reservoir attributes and reported in 

millions of barrels (MMBO):

szo =7.758(t)(hps)(f)(rfo)(ac)/(fvfo) where hps = p(1-Sw) 

where for each field simulated, the reservoir attribute values are (1) net reservoir thickness, t, in feet, (2) 

porosity, p, as a decimal fraction, (3) hydrocarbon pore space, hps, as a function of p and SW, where SW

is water saturation as a decimal fraction, (4) trapfill, f, as decimal fraction, (5) oil recovery factor, rfo, as 

a decimal fraction, (6) area of closure (ac) in thousands of acres, and (7) the oil formation volume 

factor, fvfo. The assessors provided estimates of the recovery factor (fraction of the in-place resources 

recoverable with the assumed technology), which is denoted rfo. The oil formation volume factor, fvfo,

was calculated as a function of reservoir depth (Schuenemeyer, 1999, 2005). For each size and depth 

category, an average accumulation size was computed and used as the representative field size. 

Vertical wells were assumed to have drainage areas of 160 acres (Young and Hauser, 1986). 

Development well productivity for oil (wpo) per producing well for a given individual accumulation was 

calculated by the following formula:

wpo = 7.758(t)(hps)(f)(rfo)(0.16)/(fvfo) 

The average well recoveries were calculated on the basis of the simulated play data. The average 

well productivity was classified by size class of the associated simulated accumulation. Within a given 

play, the average well productivity tends to increase as accumulation size increases. The commonality 

of plays across the central North Slope and the NPRA permitted the use of average well productivity 

measures between subareas. The well productivity data are shown in table A3-2. Table A3-2, which is 

based on the play simulations, shows that oil wells for the 1002 Area are expected to be substantially 

more productive than oil wells elsewhere. This difference can be traced to the substantial differences in 

the pay thickness attribute assessed by the geologist. On the original play forms, the median pay 

thickness for the leading oil play (Topset) in the 1002 Area was three times that of the leading oil play 

(Beaufortian Upper Jurassic Topset NE) in the NPRA (see Schuenemeyer, 1999, 2003). At the 5th 

fractile, the leading 1002 oil play has a pay thickness of over five times that of the leading oil play in the 

NPRA. 

The required number of production wells for the representative accumulation was calculated by 

dividing the recoverable accumulation volume of oil by the estimated well productivity. For 

conventional wells, each set of 10 producing wells required 4 injection wells (National Petroleum 

Council, 1981a; Young and Hauser, 1986). 
50

Table A3–2. Estimated recovery per production well, in millions of barrels of oil (MMBO), for oil accumulations by 

economic zone within study subarea as identified in text figure 4.

[NPRA, National Petroleum Reserve in Alaska; CNS, central North Slope; ANWR, Arctic National Wildlife Refuge; 

shallow <10,000 feet; deep >10,000 feet]

Discovery size 

class 

(MMBO)

NPRA CNS 1002 Area of ANWR

N110 

(MMBO)

Outside 

N110 

(MMBO)

C110 

(MMBO)

Outside 

C110 

(MMBO)

A110 

shallow 

(MMBO)

A110 

deep 

(MMBO)

A120 

shallow

(MMBO)

A120 

deep

(MMBO)

20–32 1.6 1.1 1.6 1.1 3.4 2.1 2.9 1.7

32–64 2.1 1.3 2.1 1.3 5.0 2.8 4.2 2.2

64–128 2.7 1.6 2.7 1.6 7.6 3.7 6.4 2.6

128–256 3.2 2.0 3.2 2.0 11.1 4.9 8.8 3.1

256–512 3.3 2.4 3.3 2.4 13.9 6.3 10.8 3.2

512–1,024 3.8 3.0 3.8 3.0 16.6 7.7 13.6 3.4

1,024–2,048 4.4 4.4 4.4 4.4 23.2 11.7 19.7 4.7

2,048–4,096 5.0 5.0 5.0 5.0 30.0 19.1 21.8 6.1

Application of horizontal well technology is attractive because it can reduce the number of 

production wells required to drain a pool and reduce the number of drilling pads and their sizes. It also 

tends to increase the proportion of the in-place oil that is recoverable and to increase the flow rates from 

individual wells. The drainage area and, thus, well productivity assigned to a horizontal production well 

depend on the natural drainage area of vertical wells and the length of the horizontal section of the well 

bore that is in contact with the formation. If a vertical well has a circular drainage area of 160 acres, 

then a horizontal well having a horizontal section of 3,000 feet would theoretically increase the drainage 

area to 365 acres (Joshi, 1991a,b).22 Each producing horizontal oil well is assumed to require a 

horizontal injection well. This is the case in the Alpine field (Redman, 2002) near the NPRA. This 

reconnaissance analysis cannot capture all the trade-offs in applying horizontal technologies, such as an 

increase in recoverable in-place oil and a reduction in pad costs, and so the cost estimates presented here 

may be higher than costs based on an analysis using site data. 

Gas Field Design

Gas accumulation volume (szg) was computed with the simulated reservoir attributes and 

reported in billions of cubic feet (BCF): 

szg = 4.356(t)(hps)(f)(rfg)(ac)(fvfg)*10-8, where hps = p(1-SW) 

where for each field simulated, the reservoir attribute values are (1) net reservoir thickness, t, in feet, (2) 

porosity, p, as a decimal fraction, (3) hydrocarbon pore space, hps, as a function of p and SW, where SW

is water saturation as a decimal fraction, (4) trapfill, f, as a decimal fraction, (5) gas recovery factor, rfg,

as a decimal fraction, (6) area of closure (ac) in thousands of acres, and (7) the gas formation volume 

factor, fvfg. The assessors provided estimates of the recovery factor (fraction of the in-place resource 

that is recoverable with the assumed technology), which is denoted rfg. The gas formation volume 

 22If a vertical well drains 160 acres, its expected drainage radius is 1,489 feet. The horizontal extension of the well of 3,000 

feet adds 205 acres, (3,000 ft x 2 x 1,489 ft)/(43,250 ft2

/acre), to the original 160-acre drainage area. This method of 

computing the drainage area follows Joshi (1991a). It assumes that the vertical permeability is at least equal to the horizontal 

permeability.
51

factor, fvfg, was calculated as a function of reservoir depth. For each size and depth category, the size of 

the representative discovery was the average of the discoveries in that category. 

A 1981 National Petroleum Council study (1981a, 1981b) on Arctic oil and gas development 

based its representative field designs on the assumption that the typical gas well drainage area would be 

1 square mile (640 acres). Development well productivity for gas (wpg), in billions of cubic feet per 

producing well, for an individual accumulation was calculated as: 

wpg= 4.356(t)(hps)(f)(rfg)(0.640)(fvfg)*10-8

Each gas well recovery shown in table A3-3 was computed as a volume weighted average of the 

computed well recoveries derived from the play reservoir attribute simulations for the NPRA and the 

central North Slope. Nonassociated gas has not been produced for export on the North Slope, and so 

there are no reliable data to predict the gas well performance. The required number of production wells 

for the representative accumulation was calculated by dividing the recoverable accumulation volume of 

gas by the estimated gas well productivity. Gas accumulations do not require water injection wells. 

Horizontal drilling was not applied to gas field development. 

Table A3–3. Estimated recovery per production well, in billions of cubic feet of gas (BCF), for gas accumulations 

in any economic zone.

Discovery size

class

(BCF)

Recovery per well

(BCF)

250–384 24.2

384–768 32.3

768–1,536 42.2

1,536–3,072 51.8

3,072–6,144 63.5

6,144–12,288 82.3

12,288–24,576 124.0

Drilling Costs

Total development well costs are computed as the product of the number of wells required for 

field delineation and development and of the sum of drilling, completion, and nondrilling well costs. 

Development well drilling and completion cost data were compiled from several sources, including 

industry reports (Gingrich and others, 2001; Redman, 2002; National Petroleum Council, 2003) and 

historical costs for Alaska oil wells reported in the Joint Association Survey (American Petroleum 

Institute, 1997-2005).23 Costs were estimated for representative wells within the following vertical 

intervals: as much as 5,000 feet, from 5,000 feet to 10,000 feet, from 10,000 feet to 15,000 feet, and 

greater than 15,000 feet.

The following example illustrates the cost estimation procedure for horizontal wells. Production 

wells at North Slope fields are typically drilled from gravel pads that accommodate as many as 40 well 

collars spaced at 10-foot intervals along with production equipment. Most conventional production 

wells are deviated or drilled directionally to reach target locations that are horizontally offset from the 

drilling pad. It is assumed that the directional component adds an average of 30 percent to measured 

 23In some years, the number of wells drilled in Alaska far exceeded the number of wells reported in the Joint Association 

Survey. Further, data appear to be presented in vertical depth intervals, whereas most North Slope production wells have a 

significant directional component, and so actual footage drilled is greater than vertical depth.
52

depth for drilling that is beyond the vertical depth for wells drilled with true vertical depths to 10,000 

feet. For target vertical depths of 10,000 feet and greater, the directional component requires an 

additional 20 percent of the vertical depth to reach target depth. At the target depth, a lateral extension 

of 3,000 feet is drilled and completed as a horizontal extension. If the average per-foot drilling and 

completion cost of $600 is assumed to be typical for the more accessible central North Slope areas, then 

the following equation is used to estimate horizontal development well drilling and completion costs for 

targets at a vertical depth of 10,000 feet (James Craig, Minerals Management Service, written 

communication, 2005): 

 (10,000 ft x 1.2 x $600/ft) + (3,000 ft x $600/ft) = $9.0 million per well 

In this example, the horizontal well adds 25 percent to the costs of drilling and completing a 

conventional development well, but the horizontal wells reduce the required number of producing wells 

by more than half, that is, productivity per producing well is more than doubled. Because each 

horizontal well is assumed to have one horizontal injector and the conventional well is assumed to 

require only 4 injection wells per set of 10 producers, the overall drilling investment per barrel 

recovered in the example for horizontal wells is about 89 percent of the per-barrel drilling cost 

compared to the standard well investment. To compensate for extra costs associated with drilling wells 

extending beyond 15,000 feet, it is assumed that costs increase 1 percent for each 500-foot increment in 

measured depth beyond 15,000 feet (James Craig, Minerals Management Service, written 

communication, 2008). 

Estimated costs, in 2007 dollars, by 5,000-foot depth interval for conventional wells in the 

accessible central North Slope area are $3.9 million (with vertical depth 5,000 ft), $5.9 million (7,500 

ft), $9.0 million (12,500 ft), and $14.0 million (17,500 ft). Estimated costs of corresponding horizontal 

wells with 3,000-ft lateral extensions in 2007 dollars are $5.9 million, $7.7 million, $11.4 million, and 

$17.0 million. These estimates represent average costs for drilling programs in the northern economic 

zone of the central North Slope (core area). Drilling costs are expected to be higher than the average for 

early drilling operations and lower than the average for later drilling operations in each project. 

Estimates of drilling costs for wells outside of the core area were increased to account for a lack of 

infrastructure. 

Facilities Costs—Oil and Gas Development

Production facilities include drilling pads, flow lines from drilling sites, the central processing 

unit, and infrastructure required for housing workers, including amenities. Facilities design and cost 

estimates are scaled to peak production rates and field size. As of the beginning of 2004, there were 

eight stand-alone fields operating in northern Alaska. These fields are Prudhoe Bay, Kuparuk River, 

Lisburne, Milne Point, Endicott, Badami, Northstar, and Alpine. The Liberty field, formerly Tern 

Island, was in the final planning stages for commercial development. 

There is little detailed information in the public domain about costs of facilities. An exception is 

a version of the Northstar development plan, including development cost estimates, that was submitted 

by British Petroleum Exploration (1996) to the State of Alaska for evaluation with its request for relief 

of profit-sharing provisions of the State lease. The Minerals Management Service (MMS) published the 

Liberty environmental impact statement (EIS) (Craig, 2002). A step function cost relationship that 

specified investment cost per barrel as a function of field size for the central North Slope was calibrated 

from published data and data obtained with the QUE$TOR software (IHS Inc., 2007). Table A3-4 

shows estimates of oil facilities investment costs by accumulation size class assumed for the C110 
53

economic zone of the central North Slope (text fig. 4). Facility cost estimates were increased for remote 

areas. 

Table A3–4. Estimates of oil field facilities investment costs per barrel of oil recovered by accumulation discovery 

size class for facilities located in the northernmost economic zone, C110, of the central North Slope.

[MMBO, millions of barrels of oil; $/bbl, 2007 dollars per barrel of oil]

Discovery 

size 

class

(MMBO)

Cost

($/bbl)

20–32 5.01

32–64 3.39

64–128 2.81

128–256 1.97

256–512 1.73

512–1,024 1.13

1,024–2,048 1.04

2,048–4,096 0.89

Since the mid-1980s, a number of newly discovered accumulations were developed as satellite 

units, where production fluids are processed at a nearby facility serving a larger field. The Point 

McIntyre and Niakuk accumulations share the central processing facilities at the Lisburne field. Prudhoe 

Bay production includes the following satellites: Midnight Sun, Aurora, Polaris, Borealis, and Orion. 

Kuparuk River production includes the following satellites: Tobasco, Tarn, Meltwater, and Palm. Thus 

far, nearly all of the satellite and parent fields have common ownership. The cost reduction from facility 

sharing depends on a number of factors, namely the composition of fluids, processing capacity of the 

central facility, and the relative bargaining strengths of the satellite owner and the central processing 

facilities owner. 

Recent examples demonstrate the relationships between main field facilities and satellite 

development opportunities. The central processing facility at the North Slope Alpine field currently 

processes the produced fluid mixtures (oil, gas, and water) of wells belonging to several satellite fields 

located up to 25 miles away (Nelson, 2004). For gas production, the Snohvit field in the Barents Sea 

utilizes an 88-mile multiphase pipeline from the field to an onshore processing facility. Elsewhere in the 

world in deepwater offshore areas, small accumulations, even under different ownership, are produced 

using subsea well completion technology, and their production fluids are processed at a common 

production platform or facility many miles away. The advances in multiphase flow pipeline 

management and measurement of produced fluids have enabled these cluster and satellite production 

systems to monitor production in different environments and under a variety of ownership situations 

(Atkinson and others, 2005). Consequently, it is likely that additional cluster developments and satellite 

field development strategies could be used to develop new marginally sized fields on the North Slope. 

Under some conditions, this practice will reduce the threshold size for commercial development. 

The text discusses hypothetical operations in the 1002 Area, for which the main processing 

facilities would be located outside the sensitive 1002 Area on either State or Native lands. In the 

northernmost economic zone (C110) of the central North Slope and in the northeast economic zone 

(N110) of the NPRA, discoveries of 130 million barrels or smaller are assumed to be developed as 

satellite fields. The procedure for accounting for facility-sharing charges follows an arrangement 
54

whereby it was assumed that facilities sharing would, on average, result in a 50 percent reduction in the 

initial facility investment cost for the satellite owner. The annual operating cost paid by the satellite 

owner is the sum of the annual operating cost per barrel that would be incurred if the satellite were 

developed as a stand-alone field plus the undiscounted per-barrel investment cost that was saved 

originally. Although the charges to the satellite owner resulting from this scheme could be in excess of 

the marginal costs incurred by the central processing facility operator, this scheme still reduces the 

minimum or threshold price at which a satellite becomes commercially developable while reducing risk 

as well.

Gas field facilities include pads, in-field pipelines, and other infrastructure. For gas discoveries, 

processing equipment costs are typically a smaller proportion of the total development investment 

because fluid handling and processing equipment is much less elaborate. Equipment could include gas 

dehydration and removal of other components but not an NGL plant because natural gas liquids are 

delivered through the gas pipelines to the zone hub. Table A3-5 shows the unit investment cost 

estimates by gas field size class for the economic zone C110 of the central North Slope. Facilities 

investment costs were increased for remote areas. 

Table A3–5. Estimates of gas field facilities investment costs per thousand cubic feet of gas recovered by 

accumulation size class for facilities located in the northernmost economic zone, C110, of the central North Slope.

[BCF, billion cubic feet of gas; $/MCF, 2007 dollars per thousand cubic feet]

Discovery size

class

(BCF)

Cost

($/MCF)

250–384 0.64

384–768 0.37

768–1,536 0.32

1,536–3,072 0.26

3,072–6,144 0.24

6,144–12,288 0.20

12,288–24,576 0.20

Production Profile

Oil Discoveries 

Future discoveries are assumed to attain peak annual rates of production equal to a percentage of 

the accumulation’s ultimate oil recovery. Table A3-6 lists the assumptions relating to the representative 

oil accumulation production profiles. An accumulation with less than 512 million barrels of recoverable 

oil is assumed to reach peak production in the year production starts. For accumulations with more than 

512 million barrels, peak production occurs in the second production year. Peak production is 

maintained for several years; thereafter, annual production declines 12 percent per year. 

At first glance, the 12 percent field production decline rate appears unduly steep. Observed field 

decline rates are typically more subdued because of the application of enhanced recovery techniques to 

prolong field life. However, the appropriate enhanced recovery application and its success often depend 

on site-specific conditions. Costs and production streams for oil discoveries calculated in this analysis 

include primary recovery and the application of waterflood. 
55

The volume of produced water was projected by using typical field production profiles for oil, 

the degree of field depletion, and the water-cut functions presented by Thomas and others (1991). 

Figure A3-2 shows the percentage of water expected in oil production with depletion of the field with a 

Kuparuk-type production and figure A3-3 shows the production characteristics for an Alpine-type field. 

Produced volumes of natural gas and natural gas liquids were projected by using annual oil production, 

the expected values of the gas-to-oil ratio, and NGL-to-gas ratios associated with the representative 

field’s size and depth classification.

Table A3–6. Oil discovery production profiles used in the economic analysis.

[MMBO, millions of barrels of oil]

Discovery size

class

(MMBO)

Year 

reaches 

peak

Peak as 

percent of 

recoverable

Years of 

peak 

production

20–32 1 11.00 3

32–64 1 11.00 3

64–128 1 11.00 3 

128–256 1 10.00 3

256–512 1 10.00 3

512–1,024 2 9.00 3

1,024–2,048 2 6.75 4 

2,048–4,096 2 6.50 7

Figure A3–2. Graph showing percentage of water in oil production stream as a function of reservoir depletion for 

Kuparuk-type reservoirs; data are from Thomas and others (1991).
56

Figure A3–3. Graph showing percentage of water in oil production stream as a function of reservoir depletion for 

the Alpine-type reservoirs in the National Petroleum Reserve in Alaska; data are from ARCO Alaska Inc. and others 

(1998).

Gas Discoveries

Representative gas field production profiles were developed using data from the production 

history of accumulations of similar sizes in other areas. In particular, the production histories of recent 

Gulf of Mexico fields were analyzed to determine the relationship between peak field production and 

their known recoverable gas partitioned into field size categories. With these peak production rates as a 

function of estimated field size, it was assumed that field production would be held constant until 75 to 

80 percent of the field’s original reserves is produced. The period of constant production is then 

followed by a rapid decline at a rate of 24 percent per year. These production profiles were used as an 

analog for the North Slope gas production profiles. Table A3-7 lists the gas production parameters 

assumed for this study. 

Table A3–7. Gas discovery production profiles used in the economic analysis.

[BCF, billion cubic feet of gas]

Discovery size Year Peak as Years of 

class reaches percent of peak 

(BCF)

250–384

peak

1

recoverable

7.00

production

12

384–768 2 6.50 13

768–1,536 2 6.50 13

1,536–3,072 2 6.50 13

3,072–6,144 3 6.50 14

6,144–12,288 3 6.00 14

12,288–24,576 3 6.00 14

Operating Costs

Annual operating costs include labor, supervision, overhead and administration, 

communications, catering, supplies, consumables, well service and workovers, facilities maintenance 
57

and insurance, and transportation. Some of these costs, such as well workover and labor costs, have 

declined dramatically during the last decade owing to the introduction of coiled tubing technology and 

the introduction of automation in field operations. However, the cost declines related to technology 

innovations have been partially offset by recent labor and materials cost increases.

Oil Fields

Annual operating costs, on a per-barrel-of-crude-oil basis, were estimated as a function of fluid 

volumes and number of operating wells (Craig, 2002). In particular, for the central North Slope, the 

annual oil discovery operating cost is estimated to be the sum of $2 per barrel of annual fluid flow and 

$2 million per production well per year. The produced fluids, consisting primarily of oil and water 

volumes, were projected annually using field production forecasts and water-cut functions (see figs. A3-

2 and A3-3) from Thomas and others (1991) and ARCO Alaska Inc. and others (1998), so that perbarrel costs of produced oil increased as the water cut increased and the field approached depletion. 

Water production is initially very small. Operating cost estimates were cross checked with estimates 

from the initial year cost predictions from the QUE$TOR software (IHS Inc., 2007). 

Gas Fields 

There are no commercially operating gas discoveries that export natural gas outside the North 

Slope, and so estimates of operating costs relied on data from studies based on the QUE$TOR software 

(IHS Inc., 2007). The estimates for operating costs for gas discoveries for the central North Slope are 

presented in table A3-8. 

Table A3–8. Gas field unit production cost used in the economic analysis.

[BCF, billions of c

Discovery size

class

(BCF)

250–384

ubic feet of gas; $/MCF, 2007 dollars per thousand cubic feet]

Cost

($/MCF)

1.75

384–768 1.38

768–1,536 0.80

1,536–3,072 0.50

3,072–6,144 0.37

6,144–12,288 0.26
58

Appendix 4. Federal and Alaska Taxes 

Royalties

Royalties are payments to the resource owner. The assessment area included areas where mineral 

rights were owned by the Federal Government, the Alaska State Government, and Native corporations. 

Actual royalty rates for State and Native lands can vary substantially for different parcels and periods 

depending on the economic conditions in the oil and gas industry. To simplify the analysis, it was 

assumed that each oil or gas project bore the 12.5 percent royalty payment of the gross value received at 

the wellhead to the owner of the mineral rights. This cost was modeled by assuming that royalty was 

paid in kind to the owner. 

Alaska State Taxes

Alaska’s Clear and Equitable Share Tax

The Alaska Clear and Equitable Share (ACES) tax replaced the Petroleum Production Tax (PPT) 

in 2007. The PPT had previously replaced the State severance tax in 2006. The ACES and PTT taxes are 

on the net income of the producer. Because the ACES tax is calculated from a corporate accounting 

stance, certain simplifications were needed to apply it to project analysis. The tax applies to oil, gas, and 

natural gas liquids. The tax rates are expressed in terms of barrels of oil equivalent, and so these 

commodities were converted to barrels of oil equivalent. The tax described here is specific to North 

Slope producers. 

Procedure 

The tax liability is calculated on the basis of petroleum production value (PVT) that is taxable 

and the tax rate. The taxable barrels exclude the royalty rate barrels. The corporate PVT is the product 

of the net wellhead price and taxable barrels (barrels net of royalty) minus operating costs (including 

property taxes) and capital expenditures taken that year. If the PVT is not positive, the tax liability is 4 

percent of the product of the wellhead price and taxable barrels. 

The tax rate escalates with increases in the PVT per barrel. When the PVT is positive but does 

not exceed $30 per barrel, the tax rate is 25 percent. From $30 per barrel to $92.50 per barrel, the tax 

rate increases 0.4 percent per dollar for each dollar the PVT is greater than $30 per barrel. At a PVT of 

$92.50 per barrel, the tax rate is 50 percent. The tax rate increases to a maximum rate of 75 percent from 

50 percent in steps of 0.1 percent per dollar for each dollar the PVT is greater than $92.50. 

The tax liability is the product of the tax rate and the PVT for the company. Once the tax liability 

is computed, tax credits can offset part of the taxes owed. If previous years had negative PVTs, then 25 

percent of those losses can be carried forward to later years as a tax credit. The qualified capital 

expenditures (QCE) tax credit amounts to 20 percent of the capital expenditures. The accounting 

calculation for the tax rate, tax liability, and credits is done on a corporate basis. Tax credits may be 

monetized by being sold to other North Slope operators. It should be noted that not only do corporatewide North Slope capital expenditures reduce the current year’s tax rate by reducing the PVT per barrel

but also that the 20 percent QCE credit reduces the actual net tax liability (Greg Bidwell, Alaska 

Department of Natural Resources, written communication, 2008). 
59

Application to Project Analysis 

This analysis applied the following simplified version of the tax to the project level. During 

production, the PVT, tax rates, and tax liability were computed for the single project. Initial capital for 

expenditures for field delineation and development prior to production were totaled. Twenty percent of 

this total became a tax credit against future ACES tax liability. In addition, 25 percent of the annual 

losses incurred before the start of production were carried forward as a tax credit to offset ACES tax 

liability. It was assumed that 10 percent of the annual operating costs were expenditures that qualified as 

capital expenditures (well workover and some replacement machinery). 

Ad Valorem Tax

Alaska’s ad valorem tax is 2 percent of the economic value of pipelines, facilities, and

equipment. For pipelines, a 20-year life was assumed. For tangible well costs, oil field equipment costs, 

and facilities costs, depreciation of the asset was based on the unit of production method.24 

State Income Tax

For planning purposes, the Alaska State agencies use 2 to 4 percent of net income. The rate used 

here was 4 percent of net income. Depreciation of capital assets associated with oil field development is 

permitted on a unit-of-production basis. For other capital, depreciation depends on the economic life of 

the equipment. 

State Conservation Tax

The State conservation surcharge tax was assumed to be set at $0.05 per barrel of oil. 

Federal Income Taxes

A Federal income tax rate of 35 percent of taxable income was assumed. According to the 1986 

Tax Reform Act, 30 percent of development well drilling costs is classified as tangible cost and 

therefore capitalized over 7 years. Of the remaining 70 percent of drilling cost (that is, the intangible 

drilling costs), 30 percent is depreciated over 5 years and the remaining 70 percent is expensed 

immediately.

 

 24As a practical matter, as long as the asset is operating, the basis for the tax will not be smaller than 25 percent of either

the initial investment or the asset’s estimated replacement value (Greg Bidwell, written communication, 2008).