Federal lands

Known petroleum

accumulations

NPRA

ANWR

1002 AREA

CANADA

UNITED STATES

PRUDHOE BAY

Mackenzie River

delta

Point Barrow

WILDERNESS

AREA

Northern margin

of Brooks Range

0 100 MILES

Arctic Ocean

Northern Alaska

 36 petroleum discoveries

 ~15 BBO and 35 TCFG recoverable

 commercial production

ANWR = 19 million acres

 1002 area = 1.5 million acres

 Wilderness Area = 8 million acres

NPRA = 23 million acres

Mackenzie River de

 48 petroleum discove

 ~2 BBO and 12 TCFG 

 no commercial produ

TAPS

T

he Alaska National Interest Lands Conservation Act (1980) established the Arctic National Wildlif

(ANWR) (fig. 1). In section 1002 of that act, Congress deferred a decision regarding future manage

1.5-million-acre coastal plain ("1002 area") in recognition of the area’s potentially enormous oil and gas 

and its importance as wildlife habitat. A report on the resources (including petroleum) of the 1002 area wa

mitted in 1987 to Congress by the Department of the Interior (DOI). Since completion of that report, nume

have been drilled and oil fields discovered near ANWR (fig. 2), new geologic and geophysical data have b

available, seismic processing and interpretation capabilities have improved, and the economics of North S

development have changed significantly. 

The U.S. Geological Survey (USGS) commonly is asked to provide the Federal Government with tim

scientific information in support of decisions regarding land management, environmental quality, and econ

strategic policy. To do so, the USGS must anticipate issues most likely to be the focus of policymakers in th

Anticipating the need for scientific information and considering the decade-old perspective of the petroleu

estimates included in the 1987 Report to Congress, the USGS has reexamined the geology of the ANWR 10

and has prepared a new petroleum resource assessment.

Figure 1. Map of northern Alaska and nearby parts of Canada showing locations of the Arctic National Wildlife Refuge (ANWR), the 1002 area, and 

Petroleum Reserve—Alaska (NPRA). Locations of known petroleum accumulations and the Trans-Alaska Pipeline System (TAPS) are shown, as well 

of known petroleum volumes in northern Alaska and the Mackenzie River delta of Canada. BBO, billion barrels of oil (includes cumulative productio

recoverable resources); TCFG, trillion cubic feet of gas recoverable resources.

es 

O

g

4

r 

d

t

y

ed 

n

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-028-01 (Supe

FOLD
Aichilik River

Sadlerochit Mountains

0 

Shublik Mountains

Northe

Camden Bay

Canning Ri ver

Native lands

1002 AREA

WILDERNESS AREA

Egaksrak

River

Badami

1991

1985

Kuvlum 

1993

Kemik

1969

Kavik

1969

Sourdough

1994

Undeformed area

Deformed area

Approxim

3-mile 

betwee

Federa

Marsh Creek anticline

Figure 2. Map of the ANWR 1002 area. Dashed line labeled Marsh Creek anticline marks approximate boundary between undeformed are

generally horizontal) and deformed area (where rocks are folded and faulted). Boundary is defined by Marsh Creek anticline along western 

by other geologic elements along eastern half of dashed line. Exploration wells are coded to show whether information from them was av

USGS assessment of in-place petroleum resources. Dashed red line shows the offshore extent of the entire assessment area.

ASSESSMENT PROJECT

The new assessment involved 3 years of study by 40 USGS scientists, who 

coordinated work with colleagues in other Federal agencies, Alaska State 

agencies, and several universities. New field studies were conducted, new well 

and sample data were analyzed, and new geophysical data were acquired. 

Perhaps most importantly, all 1,400 miles of seismic data that had been collected 

by a petroleum-industry consortium in 1984 and 1985 were reprocessed and 

reinterpreted. Collection of seismic data within ANWR requires an act of 

Congress, and these are the only seismic data ever collected within the 1002 

area. All this information was integrated as basic input into the petroleum 

assessment. The term "petroleum" is used herein to include crude oil, natural 

gas, and natural gas liquids. Although all petroleum commodities were assessed, 

results reported in this Fact Sheet are for crude oil only because it determines the 

economic viability of resources on the North Slope. Results for the other 

commodities are reported in a CD-ROM (USGS Open-File Report 98-34).

ASSESSMENT METHODOLOGY

The methodology used in this assessment is sligh

used in the 1987 assessment of this area when the USG

petroleum resources for the DOI Report to Congress; th

slightly modified from that used in the USGS assessme

Petroleum Reserve—Alaska (NPRA) (1979–1980). Ten 

defined as the initial step of the assessment (fig. 3). A p

that contains similar geological parameters (such as pet

and trap) that determine petroleum potential. In keeping 

responsibility for assessing the petroleum potential of a

water areas of the United States, the total play area con

the 3-mile boundary between State and Federal jurisdic

the Federal lands of the ANWR 1002 area, this assessm

associated with State waters and Native lands (fig. 2).

TRIM

TRIM
... .. . .. .

. .. . . .

Marine and nonmarine

clastic deposits

Hiatus or erosion

Marine shale

Condensed

marine shale

Limestone

and dolomite

Hue Shale

Pebble shale unit

144

208

245

286

320

360

DEVONIAN TO

PROTEROZOIC

CARBONIFEROUS

PERMIAN

TRIASSIC

JURASSIC

ELLESMERIAN SEQUENCE

Kuparuk Fm.

THOMKEMIK

UNDEFORMED

FRANKLINIAN

DEFORM

FRANKLIN

ELLESMERIAN THRUST BELT

O

G

O

BEAUFORTIAN

TH

Argillite

Granite

Basalt

Endicott

Group

Lisburne

Group

Sadlerochit

Group

Shublik Fm.

Sag River Ss.

Kingak

Shale

Kemik and

Thomson Ss.

FRANKLINIAN 

SEQUENCE

Figure 3. Summary of ages, names, and rock types present in the AN

area. The occurrence of recoverable petroleum in these rock formatio

the ANWR 1002 area is indicated by green and red circles. Gray bars a

indicate the 10 petroleum plays assessed in this study and their corre

rock formations (to the left). Note grouping of plays according to defo

undeformed areas as shown in figure 2.

recovery factor appropriate to each play was applied to the estimates of 

in-place petroleum resources to calculate technically recoverable

petroleum resources (fig. 4). 

Estimates for each play were 

aggregated to calculate total technically 

recoverable petroleum resources for the 

entire assessment area, the 1002 area, 

and the undeformed and deformed parts 

of the 1002 area (table 1). Costs associated with discovering and recovering 

petroleum resources, including the costs 

of constructing pipelines to transport 

the petroleum, were then applied to 

estimate economically recoverable

petroleum resources (fig. 4). 

Charge.—Occurrence of conditions of petroleum generation and migration adequate to cause an accumulati

of the minimum size (50 million barrels of oil (MMBO) 

in-place).

Reservoir.—Occurrence of reservoir rocks of sufficient 

quantity and quality to permit containment of petroleum 

volumes sufficient for an accumulation of the minimum 

size (50 MMBO in-place).

Trap.—Occurrence of those structures, pinch-outs, 

permeability changes, and similar features necessary fo

the entrapment and sealing of petroleum in an accumulation of the minimum size (50 MMBO in-place).

 he 95-percent 

probability level refers to 

19 in 20 chances; the 

5-percent probability 

level refers to 1 chance 

in 20 that the amounts 

shown will be at least 

that large.

T

The assessment methodology yields results that include 

probabilistic expressions of uncertainty, as illustrated schematically in 

figure 4. To stress the importance of this uncertainty, results reported 

here include 95- and 5-percent probabilities, in addition to mean value. 

The 95- and 5-percent probabilities are considered reasonable 

minimum and maximum values, and the mean is the average or 

expected value. 

FOLD
Recovery

factor Economics

Economically

recoverable

Technically

recoverable

In-place

100

75

50

25

PROBABILITY OF MORE THAN, IN PERCENT

0

VOLUME OF OIL INCREASING 

F95

F05

V1 V2

Typical view of the ANWR 1002 area coastal plain.

Figure 4. Schematic graph illustrating petroleum volumes and probabilities. Curves 

sent categories of oil in assessment. An example of how one reads this graph is illus

by the blue and orange lines projected to the curve for economically recoverable oil. 

There is a 95-percent chance (i.e., probability, F95) of at least volume V1 of economic

recoverable oil, and there is a 5-percent chance (F05) of at least volume V2 of econom

recoverable oil.

Quantities of technically recoverable oil are not 

expected to be uniformly distributed throughout the 

ANWR 1002 area. The undeformed area (fig. 2) is estimated to contain between 3.4 and 10.2 billion barrels of oil 

(BBO) (95- and 5-percent probability), with a mean of 6.4 

BBO. The deformed area (fig. 2) is estimated to contain 

between 0 and 3.2 BBO (95- and 5-percent probability), 

with a mean of 1.2 BBO. 

Figure 5 shows the expected numbers of 

accumulations and volumes of technically recoverable oil 

grouped by accumulation-size class. It shows that most of 

the oil is estimated to occur in accumulations that exceed 

100 million barrels, the size of recently developed north 

Alaskan stand-alone 

accumulations. Moreover, at the mean, nearly 

80 percent of the oil is 

thought to occur in the 

western part of the 

ANWR 1002 area, which 

is closest to existing 

infrastructure. Volumes 

of oil are expected to 

occur as several 

accumulations rather 

than a single large 

accumulation.

Commercial 

viability of a discovery 

depends on oil price, 

accumulation size, 

recovery technology, and 

proximity to existing 

infrastructure (pipelines, 

etc.). The economic 

analysis presents the cost of transforming technically 

recoverable resources into producible proved reserves—it 

shows the market price that would have to be paid to find, 

develop, produce, and transport to market (lower 48 West 

Coast) any particular quantity of assessed oil assuming 

current technology and existing scientific understanding. 

Figure 6, which is based on the field-size distributions 

associated with the mean, 95-, and 5-percent probability 

oil estimates, summarizes the findings of the economic 

analysis. The cost functions are calculated in constant 

1996 dollars and are based on the expectation that production will repay all operating costs, including taxes and 

transport to market, all investment expenditures, and 

provide and an after-tax rate of return of at least 12 

percent on the investment.

 Undeformed part 3,403 6,420 10,2

 Deformed part 0 1,248 3,

1 Includes 1002 area shown on figure 2, Native lands, and adjacent State water areas within 3-mil

 boundary (see fig. 2).

In-place resources.—The amount 

of petroleum contained in 

accumulations of at least 50 

MMBO without regard to 

recoverability.

Technically recoverable 

resources.—Volume of petroleum 

representing that proportion of 

assessed in-place resources that 

may be recoverable using current 

recovery technology without 

regard to cost.

Economically recoverable 

resources.—That part of the 

technically recoverable resource 

for which the costs of discovery, 

development, and production, 

including a return to capital, can 

be recovered at a given well-head 

price.

FOLD
0

5

NUMBER OF 

8–16

16–3232–64

64–128

128–256

256–512

512–1,024

1,024–2,048

2,048–4,0964,096–8,192

8–16

16–3232–64

64–128

128–256

256–512

512–1,024

1,024–2,048

2,048–4,0964,096–8,192

500

1,000

1,500

2,000

2,500

VOLUME OF OIL, IN MILLIONS OF BARRELS

0

TECHNICALLY RECOVERABLE OIL GROUPED BY ACCUMULATION-SIZE CLASS,

IN MILLIONS OF BARRELS

B

non-Federal. Adding the accumula

undeformed area to those of the d

size category gives the total numb

accumulations for the entire assess

plus non-1002).

B, Histogram showing the expecte

oil estimated to exist in each accum

of technically recoverable oil resou

category, histogram bar on left is f

and bar on right is for deformed ar

bar is divided into Federal and non

The histogram is read as follows: I

undeformed area contains approxi

barrels of technically recoverable o

containing between 512 and 1,024 

technically recoverable oil; approx

is Federal and approximately 500 M

Adding the volume of oil in the un

of the deformed area for each size 

total volume of those sized accumu

assessment area (1002 area plus n

Photograph of oil-stained sandstone near crest of 

Marsh Creek anticline, 1002 area.

TRIM

TRIM
area 

of 

gory 

e 

ea 

m 

the 

on 

ns 

BO 

eral. 

that 

e 

tire 

and 5-percent probabilities) and mean values are 20.7 BBO versus 13.8 BBO 

(current assessment compared to 1987 assessment). The increase results in large 

part from improved resolution of reprocessed seismic data, which allowed the 

identification of many more potential petroleum accumulations in parts of the 

area, and analog information provided by recent nearby oil discoveries.

Another significant change is in the geographic distribution of resources. 

In the 1987 assessment, about 75 percent of the mean estimated in-place oil was 

in the southeastern or deformed area and only 25 percent was in the northwestern or undeformed area (fig. 2). In the current assessment, nearly 85 percent 

of the in-place oil is in the undeformed area and only about 15 percent is within 

the deformed area. Again, the reason is largely related to improved resolution of 

the seismic data, especially in the undeformed area where, in various plays, it 

allowed the identification of many more potential petroleum accumulations than 

were previously thought to exist. The southeastern area—with only a single well 

offshore and complex geology onshore—carries great uncertainty. Further, part 

of that area considered oil prospective in 1987 is now considered prospective 

only for gas because of new understanding of the thermal history of the rocks.

 he U.S. Geological Surv

 responsible for the inpu

this assessment. The USGS a

cooperation of the U.S. Fish 

Service, Bureau of Land Ma

Management Service, and th

Department of Natural Reso

and Geophysical Surveys, D

Gas, and Oil and Gas Conse

Commission), which provide

well as feedback on geology 

T 

or further information and to request a C

 (USGS Open-File Report 98-34) containing de

and supporting scientific documentation, sen

gd-energyprogram@usgs.

or contact:

Kenneth J. Bird kbird@usgs.gov (650) 3

David W. Houseknecht dhouse@usgs.gov (7

FF

(mean value), which is distributed among 10 plays. Most of t

to occur in the western, undeformed part of the ANWR 1002 

closest to existing infrastructure. Furthermore, the oil is expe

number of accumulations rather than a single large accumula

economically recoverable oil, expressed by probability curve

amounts of oil with increasing price. At prices less than $13 p

commercial oil is estimated, but at a price of $30 per barrel, b

billion barrels are estimated. Economic analysis includes the 

developing, producing, and transporting oil to market based o

after-tax return on investment, all calculated in constant 1996 

The amounts of in-place oil estimated for the ANWR 1

than previous USGS estimates. The increase results in large p

resolution of reprocessed seismic data and geologic analogs p

nearby oil discoveries.

EXPLANATION OF WHY A REVISED FACT SHEET

IS BEING ISSUED AND WHAT HAS CHANGED:

This revised Fact Sheet is being issued in order to prov

complete summary of the 1998 USGS oil and gas assessment 

National Wildlife Refuge 1002 Area. The original Fact Sheet 

hard-copy executive summary intended for distribution coinc

1998 public announcement of the assessment results. Printing 

completion of the Fact Sheet before completion of the final ec

Accordingly, only a general and relatively conservative discu

resources was included. This update replaces that general eco

with a summary of the completed economic analysis, one tha

part of the overall documentation of the assessment provided 

File Report 98-34. In addition, two 

typographical errors in the original 

Fact Sheet have been corrected: In 

figure 1, the recoverable northern 

Alaska gas amount is changed from 

45 TCFG to 35 TCFG. In table 1, 

the mean volume of oil estimated 

for the entire assessment area is 

changed from 10,322 million 

barrels to 10,360 million barrels. 

Figure 6. Summary of the USGS estimates of economically recoverable oil 

that may occur beneath the Federal part of the Arctic National Wildlife 

Refuge 1002 Area. The three curves are based on estimates of technically 

recoverable oil volumes at the mean (expected) value, and at the 95 percent 

(F95) and 5 percent (F05) probabilities. Each curve relates market price/cost 

to the volume of oil estimated to be profitably recoverable. Included are the 

costs of finding, developing, producing, and transporting oil to lower 48 

West Coast market based on a 12 percent after-tax return on investment all 

calculated in constant 1996 dollars. The chart is read as follows: At a market 

price of $24 per barrel, there is a 95 percent probability of at least 2.0 BB of 

economically recoverable oil and a 5-percent probability of at least 9.4 BB. 

The mean or expected value is at least 5.2 BB of economically recoverable 

oil at $24 per barrel.

FOLD

0 

10 

20 

30 

40 

MARKET PRICE, IN DOLLARS PER BARREL

0 2 4 6 8 10 

BILLIONS OF BARRELS OF OIL

RESOURCE COSTS—ANWR 1002 AREA

F95

MEAN

F05