U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2009–3060

July 2009

National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Hydrocarbon Resources 

of the Western Oregon and Washington Province

Printed on recycled paper

Using a geology-based assessment methodology, the 

U.S. Geological Survey estimated mean volumes of 

2.2 trillion cubic feet (TCF) of undiscovered natural 

gas and 15 million barrels of oil (MMBO) in the 

Western Oregon and Washington Province. More 

than 67 percent, or 1.5 TCF, of the undiscovered natural gas is continuous gas estimated to be coalbed gas 

in Tertiary coals in western Oregon and Washington.

Introduction

The U.S. Geological Survey (USGS) recently completed 

an assessment of the undiscovered, technically recoverable 

oil and gas resources of the Western Oregon and Washington 

Province (fig. 1). The province includes all of Oregon and 

Washington north of the Klamath Mountains and west of the 

crest of the Cascade Range. It extends offshore to the 3-mi limit 

of State waters on the west and to the International Boundary in 

the Straits of Juan de Fuca and Canada on the north. The province 

measures about 450 mi north-south and 50 to 160 mi east-west, 

encompassing more than 51,000 mi2

 (fig. 1).

The assessment of the Western Oregon and Washington 

Province is geology based and used the total petroleum system 

(TPS) concept. The geologic elements of a TPS 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 

two conventional and one unconventional (continuous) total 

petroleum systems with one assessment unit (AU) in each TPS: 

(1) the Cretaceous-Tertiary Composite TPS and the Western 

Oregon and Washington Conventional Gas AU, (2) the Tertiary 

Marine TPS and the Tertiary Marine Gas AU, and (3) the Tertiary 

Coalbed Gas TPS and the Eocene Coalbed Gas AU, in which a 

cell-based methodology was used.

The province (fig. 1) occupies a complex geologic setting 

along the northwest continental margin of North America. Some 

5,000 ft to more than 23,000 ft of Paleogene volcanic rocks, 

marine mudstone and arkosic and lithic sandstone, and nonmarine 

arkosic and lithic sandstone, mudstone, carbonaceous shale, and 

coal are present in western Oregon and Washington; these rocks 

include potentially mature source rocks and reservoir rocks.

Before 1979, the only oil and gas production was in the 

Washington part of the province, near Grays Harbor, from 1957 to 

1961 (fig. 1) where about 12,000 barrels of oil and associated gas 

were produced. Currently, the only hydrocarbon production within 

the province is from the Mist gas field in northwestern Oregon 

(fig. 1) that was discovered in May 1979. The Mist field has 

produced about 65 billion cubic feet of gas (BCFG) from upper 

Eocene Cowlitz Formation reservoirs through 2008.

Resource Summary

The USGS assessed both undiscovered technically recoverable conventional oil and gas and continuous (unconventional) 

coalbed gas in the Western Oregon and Washington Province 

(table 1), resulting in an estimated total mean of 2.2 trillion 

cubic feet of gas (TCFG) and a mean of 15 million barrels of oil 

(MMBO). More than 67 percent of the total mean gas (1.5 TCFG) 

is contained within the hypothetical Eocene Coalbed Gas AU, 

Figure 1. Western Oregon and Washington Province located in 

western Oregon and Washington; boundary is shown in red. CretaceousTertiary Total Petroleum System (TPS) is shown in orange. Tertiary Coalbed 

Gas TPS is shown in dark blue. Tertiary Marine TPS shown in dark green.

Eastern Oregon and Washington Province boundary is shown in yellow

(Brownfield, 2008). Location of the Coos Bay coal field shown as a solid

brown oval and the Mist gas field shown as a red circle.

WASHINGTON

OREGON

NEVADA

MT

IDAHO

CALIFORNIA

CANADA

Yakima

Spokane

Richland

Portland

Eugene

PACIFIC

OCEAN

Columbia

River

Banks 

Lake

Coeur 

d'Alene 

Lake

Lake 

Pend 

Oreille

Malheur 

Lake

Potholes

Reservoir

Crater

Lake

Mist

gas field

§ ̈¦5

§ ̈¦84

§ ̈¦84

§ ̈¦82

§ ̈¦90

§ ̈¦90

0 60 MILES

WA

OR

NV

ID

CA

CANADA

125° 123° 121° 119° 117° 115°

42°

44°

46°

48°

50°

Coos 

Bay

Coos 

Bay

coal

field

Seattle

Bellingham

Olympic

Peninsula

Grays Aberdeen Harbor

§ ̈¦5
which encompasses an area of more than 11 million acres. In this 

continuous AU the Eocene coals, such as the coal-bearing Eocene 

Coaledo Formation (fig. 2) serve as both the source rock and 

reservoir. Within the Western Oregon-Washington Conventional 

Gas AU the USGS estimated a mean volume of 454 BCFG. An 

estimated mean volume of 15 MMBO of conventional oil and 

725 BCFG is in the Tertiary Marine AU, which contains Paleogene 

turbidite rocks (fig. 3). In this assessment unit there are numerous 

gas and oil seeps, and the potential source rocks are marine shales 

and the reservoir rocks are arkosic and lithic turbidite sandstones.

For Additional Information

Supporting geologic studies of Total Petroleum Systems 

and Assessment Units, and reports on the methodology used in 

the Western 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/.

Total Petroleum System (TPS)

and Assessment Unit (AU)

Field

Type

Total Undiscovered Resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

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

Cretaceous-Tertiary Composite TPS

Western Oregon–Washington

Conventional Gas AU

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

Gas 79 403 1,000 454 0 1 2 1

Tertiary Marine TPS

Tertiary Marine Gas AU Oil 2 9 45 15 3 14 70 22 0 1 4 1

Gas 34 195 646 249 1 5 17 6

Total Conventional Resources 2 9 45 15 116 612 1,716 725 1 7 23 8

Tertiary Coalbed Gas TPS

Eocene Coalbed Gas AU CBG 0 0 0 0 565 1,307 3,024 1,489 0 0 0 0

Total Continous Resources 0 0 0 0 565 1,307 3,024 1,489 0 0 0 0

Total Undiscovered 

Oil and Gas Resources

2 9 45 15 681 1,919 4,740 2,214 1 7 23 8

Table 1. Western 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 

accumulations, all liquids are included as the NGL (natural gas liquids). Undiscovered gas resources are the sum of non-associated and associated gas. F95 represents 

a 95 percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under assumption of perfect correlation. TPS, total 

petroleum system; AU, assessment unit; CBG, coabed gas. Gray shade indicates not applicable.]

Figure 2. Outcrop of part of the deltaic lower member of the middle 

Eocene Coaledo Formation at Sunset Bay State Park, near Coos Bay, 

Oregon (fig. 1). Soft sediment deformation can be seen in the center 

of the photo. Strata are dipping eastward toward the trough of the 

South Slough syncline in the Coos Bay coal field (fig. 1).

Western Oregon and Washington Province 

Assessment Team:

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

Ronald R. Charpentier, Troy A. Cook, Timothy R. Klett, 

Richard M. Pollastro, and Christopher J. Schenk.

References

Brownfield, M.E., 2008, Chapter 2–Cretaceous-Tertiary 

composite total petroleum system and geologic assessment 

of undiscovered gas resources of the Eastern Oregon and 

Washington Province, in U.S. Geological Survey Eastern 

Oregon and Washington Assessment Team, Geologic assessment of undiscovered gas resources of the eastern Oregon 

and Washington province: U.S. Geological Survey Digital 

Data Series DDS–69–O, 43 p.

Figure 3. Upper Eocene turbidite sandstone rocks along the 

northwest shore of the Olympic Peninsula, northwestern Washington. 

Cape Flattery is in the distance. Turbidite units are potential reservoirs 

within the Tertiary Marine TPS and the Tertiary Marine Gas AU.