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U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet 2004–3121

December 2004

Oil and Gas Assessment of Yukon Flats, 

East-Central Alaska, 2004

The U.S. Geological Survey (USGS) 

recently completed a new assessment 

of undiscovered oil and gas resources 

for the Yukon Flats Tertiary Composite 

Total Petroleum System in east-central 

Alaska. The assessment indicates the 

probable existence of technically recoverable oil and gas resources, with 

mean estimates of about 5.5 trillion 

cubic feet of undiscovered natural gas, 

173 million barrels of undiscovered oil, 

and 127 million barrels of natural-gas 

liquids in conventional accumulations.

Introduction

Yukon Flats is a region of low, forested 

hills and fl atlands with numerous streams 

and lakes, situated generally to the east of 

the Trans-Alaska Pipeline System in eastcentral Alaska. U.S. Geological Survey 

(USGS) scientists recently fi nished their 

fi rst detailed assessment of the undiscovered oil and gas potential of the Yukon Flats 

region. Previously, the region s potential 

had been assessed only as a part of larger 

oil and gas assessments for central Alaska.

At present, there is no commercial 

petroleum production in the Yukon Flats 

region, but the new USGS assessment 

indicates the probable existence of technically recoverable oil and gas resources—in 

other words, those resources that can be 

discovered, developed, and produced 

by using current technology—in rocks 

of Tertiary age (about 1.8 to 65 million 

years old). The assessment was based 

on the general geologic elements used to 

defi ne a Total Petroleum System (TPS), 

which include hydrocarbon source rocks 

(source-rock maturation, hydrocarbon 

generation, and hydrocarbon migration), 

reservoir rocks (sequence stratigraphy and 

petrophysical properties), and hydrocarbon traps (trap formation and timing). The 

Yukon Flats TPS is a “composite” petroThe 13,500-squaremile (35,000 km2

) 

Yukon Flats assessment area is 

characterized by 

low, forested hills, 

fl atlands, meadows, meandering 

streams, and lakes. 

This photograph, 

taken northwest 

of Circle, Alaska, 

shows a typical 

landscape of the 

region.

!,!3+!

!REA

OFMAP

National Assessment of Oil and Gas Fact Sheet

U.S. Geological Survey scientists recently fi nished their fi rst detailed assessment of the undiscovered oil and gas potential of the 

Yukon Flats Tertiary Composite Total Petroleum System (red outline) 

of east-central Alaska. The assessment indicates the probable 

existence of technically recoverable oil and gas resources.
Printed on recycled paper

leum system because available geologic 

evidence suggests that it contains multiple 

horizons of petroleum source rocks—including shale, mudstone, and coal of 

Tertiary and Mesozoic age—rather than a 

single horizon of source rock, as in some 

other petroleum systems of the world.

Using this geologic framework, the 

USGS defi ned four Assessment Units 

within the Yukon Flats Tertiary Composite 

TPS—the Tertiary Sandstone Assessment 

Unit, the Subthrust Assessment Unit, the 

Crooked Creek Assessment Unit, and the 

Coalbed Gas Assessment Unit. Undiscovered, conventional oil and gas resources 

were quantitatively assessed for the Tertiary Sandstone, Subthrust, and Crooked 

Creek Assessment Units. The Coalbed 

Gas Assessment Unit, which may contain 

continuous (unconventional) gas resources, 

was not quantitatively assessed for this 

study and will be considered at a future 

date, along with other potential coalbedgas units in Alaska.

Resource Summary

The USGS assessment strategy provides estimates of the volumes of undiscovered petroleum (mainly oil, gas, and 

natural-gas liquids) that are technically 

recoverable and that have the potential to 

be added to reserves in a 30-year forecast 

span. For the Yukon Flats Tertiary Composite Total Petroleum System, the USGS 

estimates a mean of 5.46 trillion cubic 

feet of gas (TCFG), a mean of 172.66 

million barrels of oil (MMBO), and a 

mean of 126.67 million barrels of natural-gas liquids (MMBNGL). Nearly all 

of these undiscovered resources are estimated to be within the Tertiary Sandstone 

Assessment Unit. Of the 5.46 TCGF of 

undiscovered gas at the mean, about 97% 

(5.28 TCGF) is believed to be within the 

Tertiary Sandstone Assessment Unit, less 

than 1% (0.02 TCGF) is in the Subthrust 

Assessment Unit, and about 3% (0.16 

TCGF) is in the Crooked Creek Assessment Unit. Of the 172.66 MMBO of 

undiscovered oil at the mean, about 96% 

(165.57 MMBO) is believed to be within 

the Tertiary Sandstone Assessment Unit, 

less than 1% (0.61 MMBO) is in the Subthrust Assessment Unit, and about 4% 

(6.47 MMBO) is in the Crooked Creek 

Assessment Unit.

For Further Information

Supporting geologic studies of the Yukon Flats Tertiary 

Composite Total Petroleum System and the Assessment 

Units, and the methodology used in the Yukon Flats assessment, are in preparation. Assessment results are available at 

the USGS Central Energy Team Web site, 

http://energy.cr.usgs.gov/oilgas/noga/.

or contact

Richard G. Stanley: rstanley@usgs.gov (650) 329–4918

This Fact Sheet and any updates to it are available online at

http://pubs.usgs.gov/fs/2004/3121/

Richard G. Stanley, Thomas S. Ahlbrandt;

 Ronald R. Charpentier, Troy A. Cook, 

Jesse M. Crews, Timothy R. Klett, Paul G. Lillis, 

Robert L. Morin, Jeffrey D. Phillips,

 Richard M. Pollastro, Elisabeth L. Rowan, 

Richard W. Saltus, Christopher J. Schenk, 

Megan K. Simpson, Alison B. Till, 

and Sandra M. Troutman

Edited by James W. Hendley II

Graphic design by Susan Mayfi eld and Sara Boore

Assessment Unit Accumulation

type

MAS Prob. 

(0-1)

Total undiscovered resources

Oil (MMBO) Gas (BCFG) Natural-gas liquids (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Tertiary Sandstone

Oil 0.5 0.81 0.00 106.77 560.35 165.57 0.00 103.49 565.05 165.80 0.00 6.04 34.46 9.97

Gas 3 0.00 4,629.17 12,862.56 5,117.36 0.00 98.15 295.67 112.51

Subthrust

Oil 0.5 0.24 0.00 0.00 3.39 0.61 0.00 0.00 3.36 0.61 0.00 0.00 0.20 0.04

Gas 3 0.00 0.00 92.91 15.94 0.00 0.00 2.04 0.35

Crooked Creek

Oil 0.5 0.48 0.00 0.00 28.75 6.47 0.00 0.00 29.06 6.55 0.00 0.00 1.76 0.40

Gas 3 0.00 0.00 714.96 156.36 0.00 0.00 15.89 3.42

Coalbed Gas Gas Not quantitatively assessed

Total undiscovered 

oil and gas 

resources

0.00 106.77 592.48 172.66 0.00 4,732.66 14,627.89 5,462.63 0.00 104.18 350.02 126.67

Photograph looking northward across the Trans-Alaska Pipeline System, showing low, forested hills along the 

Yukon River (right-hand edge of photo), near the west edge of the Yukon Flats assessment area. 

Yukon Flats Tertiary Composite Total Petroleum System assessment results.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids; MAS, minimum accumulation size assessed [MMBO 

or BCFG]; Prob., probability of at least one accumulation equal to or greater than the MAS. Results shown are fully risked estimates. For gas fi elds, all liquids are 

included under the natural gas liquids category. F95 denotes a 95% chance of at least the amount tabulated. Other fractiles are defi ned similarly. Fractiles are additive only under the assumption of perfect positive correlation. Shading indicates not applicable.]