Figure 1.  Area of Eastern Oregon and Washington Province located in northcentral and northeastern Oregon and eastern Washington. Province boundary

shown in red. Cretaceous-Tertiary Composite Total Petroleum System is shown

in blue.

Lake Harney

Malheur

Lane

Grant

Klamath

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Linn

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Clallam

Whatcom

Wheeler

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Polk Marion

Clackamas

Skamania

Josephine

Cowlitz

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Tillamook

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Clatsop

Asotin

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Columbia

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Sherman

Thurston

Washington

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Oreille

Hood Multnomah River

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U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006–3091

July 2006

National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Gas Resources of the Eastern 

Oregon and Washington Province, 2006

Printed on recycled paper

Introduction

The U.S. Geological Survey (USGS) recently 

completed an assessment of the undiscovered gas 

resources of the Eastern Oregon and Washington 

Province; the province includes about 60,000 mi2

in eastern Oregon and Washington (fig. 1). The 

assessment of the Eastern Oregon and Washington 

Province was geology based and used the total 

petroleum system (TPS) concept. The geologic 

elements of a total petroleum system include 

hydrocarbon source rocks (source rock maturation, and hydrocarbon generation and migration), 

reservoir rocks (quality and distribution), and 

traps for hydrocarbon accumulation. Using these 

geologic criteria, the USGS assessment team 

defined the Cretaceous-Tertiary Composite Total 

Petroleum System. Three assessment units (AU) 

were defined within the TPS, and undiscovered 

gas resources within two of the three assessment 

units were quantitatively estimated (table 1).

Volcanic rocks in the Columbia River Basalt 

Group, which range in thickness from 4,000 

to 13,000 ft, overlie a nonmarine sedimentary 

rock succession in much of the Eastern Oregon 

and Washington Province area. Some 5,000 

to 10,000 ft of arkosic sandstone, mudstone, 

lacustrine shale, and coal are known to be present 

below the basalt in north-central Oregon and 

central Washington; these rocks include potential 

source and reservoir rocks.

Using a geology-based assessment 

methodology, the U.S. Geological Survey 

estimated a mean of 2.4 trillion cubic feet (TCF) 

of undiscovered natural gas in the Eastern Oregon 

and Washington Province. More than 90 percent, 

or 2.1 TCF, of the estimated undiscovered natural 

gas is continuous gas estimated to be trapped in 

Tertiary rocks overlain by the Columbia River 

Basalt Group.
Resource Summary

The USGS assessed both undiscovered 

conventional gas and undiscovered continuous 

(unconventional) gas in the Eastern Oregon and 

Washington Province (table 1), resulting in an 

estimated mean total of 2.4 trillion cubic feet of 

gas (TCFG) and 9.8 million barrels of natural 

gas liquids (MMBNGL) (table 1). More than 

90 percent (2.1 TCFG) is contained within the 

hypothetical Columbia Basin Continuous Gas 

AU, which encompasses an area of more than 

4 million acres. Undiscovered resources within this 

AU are considered to be within an overpressured, 

continuous accumulation of gas trapped within 

Tertiary rocks that are overlain by the Columbia 

River Basalt Group. An estimated 300 billion 

cubic feet (BCF) of conventional gas is present in 

the hypothetical Eastern Oregon and Washington 

Conventional Gas AU, which contains more 

than 22.2 million acres. Potential reservoir and 

source rocks are known or inferred to coexist in 

this assessment unit, although thick Miocene to 

Holocene volcanic sequences cover the reservoir 

and source rock intervals. The Republic Graben 

Assessment Unit, the third AU defined, was not 

quantitatively assessed.

For Additional Information

Supporting geologic studies of total petroleum systems and assessment units, and reports on 

the methodology used in the Eastern Oregon and 

Washington Province assessment, are in progress. 

Assessment results are available at the USGS 

Central Energy Team website: http://energy.cr.usgs.

gov/oilgas/noga/.

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

Oil 0 0 0 0 0 0 0 0 0 0 0 0

Gas 

Gas 

0 242 857 305 0 0.41 1.94 0.61

1,179 2,013 3,436 2,122 3.12 7.85 19.79 9.20

0 0 0 0 1,179 2,255 4,293 2,427 3.12 8.26 21.73 9.81

Total Undiscovered Oil and

Gas Resources 

Cretaceous-Tertiary

Composite TPS

 Total undiscovered resources

Eastern Oregon and Washington 

Conventional Gas AU

Republic Graben Gas AU

Columbia Basin 

Continuous Gas AU

Gas (BCFG) NGL (MMBNGL) Field 

type

Total Petroleum Systems 

(TPS) 

and Assessment Units (AU)

Oil (MMBO)

Table 1. Eastern Oregon and Washington Province assessment results. 

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates.

For gas fields, all liquids are included under the NGL (natural gas liquids) category. Undiscovered gas resources are the sum of nonassociated and 

associated gas. F95 represents a 95 percent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive

under the assumption of perfect positive correlation. Gray shade indicates not applicable] 

Not quantitatively assessed

Figure 2.  Columbia River Basalt Group and the Columbia River,

looking north from the Oregon side of the river. The town of Lyle,

Washington, is visible on left side of photograph.

Eastern Oregon and Washington 

Province Assessment Team

Michael E. Brownfield (mbrownfield@usgs.gov), Marilyn 

E. Tennyson, Thomas S. Ahlbrandt, Ronald R. Charpentier, 

Troy A. Cook, Timothy R. Klett, Richard M. Pollastro, and 

Christopher J. Schenk.