U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3091

February 2018

National and Global Petroleum Assessment

Assessment of Undiscovered Conventional Oil and Gas Resources in the 

Wyoming Thrust Belt Province, Wyoming, Idaho, and Utah, 2017

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean undiscovered, technically recoverable resources 

of 26 million barrels of oil and 700 billion cubic feet of gas in the Wyoming Thrust Belt Province, Wyoming, Idaho, and Utah.

Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the 

potential for undiscovered, technically recoverable conventional oil and 

gas resources in the Wyoming Thrust Belt Province, which is located 

west of the Southwestern Wyoming Province, east of the Eastern Great 

Basin Province, south of the Idaho-Snake River Downwarp Province, 

and north of the Uinta-Piceance Basin Province (fig. 1). The Wyoming 

Thrust Belt developed by east-directed compression associated with 

steeply dipping subduction during the Late Jurassic to Late Cretaceous 

Sevier Orogeny (Lamerson, 1982; Webel, 1987). Compression resulted 

in a series of stacked thrust sheets that are progressively younger in 

age to the east. The major thrusts in the Wyoming Thrust Belt Province 

are the Paris-Willard, Meade, Crawford, Absaroka, Hogsback-Darby, 

and Prospect (fig. 1). Exploration in the 

mid-1970s resulted in the discovery of 

more than 30 oil and gas fields, most of 

which are associated with the Absaroka 

thrust sheet. Compared to the Absaroka, 

exploration along the other thrust sheets 

has been largely unsuccessful. The 

temporal sequence of thrust loading 

and structural deformation has resulted 

in a complex evolution of petroleum 

systems in the Wyoming Thrust Belt 

Province (Warner, 1982; Edman and 

Surdam, 1984; Burtner and Nigrini, 

1994).

Total Petroleum System and 

Assessment Unit

The USGS defined the Paleozoic–

Mesozoic Composite Total Petroleum 

System (TPS) and the Wyoming 

Thrust Belt Conventional Oil and Gas 

Assessment Unit (AU) within this TPS. 

The Paleozoic–Mesozoic Composite 

TPS includes petroleum generated 

from organic-rich shales of the Lower 

Permian Phosphoria Formation and 

the Lower Cretaceous Aspen Shale 

(equivalent to the Mowry Shale). 

Organic-rich shales of the Phosphoria 

Formation contain Type IIS marine 

organic matter (Lillis and Selby, 2013), 

have total organic carbon (TOC) contents averaging 4 weight percent even 

with high levels of thermal maturation 

(Burtner and Nigrini, 1994), and are as 

much as 50 meters (m) thick (Maughan, 

1984). Aspen Shale contains Type II and 

Type I organic matter, has TOC contents 

up to 3 weight percent (Warner, 1982), 

Figure 1. Map showing the location of one conventional assessment unit (AU) in the Wyoming 

Thrust Belt Province, Wyoming, Idaho, and Utah.

and ranges up to 20 m thick. The Wyoming Thrust Belt Conventional 

Oil and Gas AU was defined to include gas and minor oil from the 

Phosphoria Formation and oil and gas from the Aspen Shale.

The assessment input data are summarized in table 1.

Geologic Model for Assessment

The geologic model for undiscovered conventional oil and gas 

resources in the Wyoming Thrust Belt Conventional Oil and Gas AU 

includes gas and minor oil generated from the Phosphoria Formation 

and oil and gas from the Aspen Shale that migrated into conventional 

reservoirs within structural traps. Phosphoria Formation shales are interpreted to have reached thermal maturity for oil generation prior to the 

development of most thrust-related structures (Warner, 1982; Burtner 

GREAT

SALT 

EASTERN GREAT LAKE

BASIN PROVINCE

SOUTHWESTERN

WYOMING PROVINCE

WIND RIVER

BASIN PROVINCE

IDAHO-SNAKE RIVER

DOWNWARP PROVINCE

UINTA-PICEANCE

BASIN PROVINCE

BIGHORN BASIN

PROVINCE

43°

42°

41°

Base map from U.S. Department of the Interior National Park Service

0 25 50 KILOMETERS

0 25 50 MILES

EXPLANATION

Wyoming Thrust Belt Conventional Oil and Gas AU

Province boundary

Thrust faults

PARIS-WILLARD

THRUST FAULTS

MEADE

THRUST

FAULT

PROSPECT

THRUST

FAULT

HOGSBACK-DARBY

THRUST FAULTS

ABSAROKA

THRUST

FAULT

CRAWFORD

THRUST

FAULT

IDAHO

UTAH COLORADO

WYOMING

NEVADA

MONTANA

Map

area

WYOMING

THRUST BELT

PROVINCE

–114° –113° –112°

UTAH

NEVADA

IDAHO

WYOMING

COLORADO

SALT LAKE 

CITY

Pocatello

Green River

–111° –110° –109° –108°
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173091

Wyoming Thrust Belt Province Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Marilyn E. Tennyson, Cheryl A. Woodall, Michael E. Brownfield, Phuong A. Le, Timothy R. Klett, 

Stephanie B. Gaswirth, Thomas M. Finn, Kristen R. Marra, and Heidi M. Leathers-Miller

For More Information

Assessment results are also available at the USGS Energy Resources Program website at https://energy.usgs.gov.

and Nigrini, 1994), and much of the Phosphoria Formation oil migrated eastward into traps in what are now the Laramide basins in Wyoming, 

Montana, and Colorado (Lillis and Selby, 2013). Following oil migration, any oil retained within the Phosphoria Formation shales in the Wyoming 

Thrust Belt Province would have cracked to dry gas from thrust loading that occurred throughout Sevier and Laramide deformation. Most of the 

Phosphoria Formation shales in the thrust belt are now within the thermal window for dry gas or are postmature for gas (Edman and Surdam, 1984).

The Lower Cretaceous Aspen Shale reached thermal maturity for generation of oil and gas coincident with movement of the major thrust sheets 

during the Sevier Orogeny (Warner, 1982; Edman and Surdam, 1984; Burtner and others, 1994). These shales are the primary source for oil in the 

conventional reservoirs of the thrust belt, but gas has also been generated from the Aspen Shale (Warner, 1982).

Reservoir rocks are mainly carbonates within the Ordovician Bighorn Dolomite, the Mississippian Madison Group, Pennsylvanian Amsden 

Formation, Lower Permian Phosphoria Formation, Lower Triassic Thaynes Formation, Middle Jurassic Twin Creek Limestone, Pennsylvanian Weber 

and Tensleep Sandstones, and Jurassic Nugget Sandstone.

Table 1. Key assessment input data for one conventional assessment unit 

in the Wyoming Thrust Belt Province, Wyoming, Idaho, and Utah.

[AU, assessment unit; MMBO, million barrels of oil; BCFG, billion cubic feet of gas. 

Shading indicates not applicable]

Assessment input data Wyoming Thrust Belt Conventional Oil and Gas AU

Minimum Median Maximum Calculated mean

Number of oil fields 1 10 30 10.6

Number of gas fields 1 40 120 42.5

Sizes of oil fields (MMBO) 0.5 1.0 100 2.5

Sizes of gas fields (BCFG) 3 6 600 14.9

AU probability 1.0

Table 2. Assessment results for one conventional assessment unit in the Wyoming Thrust Belt Province, Wyoming, Idaho, and Utah. 

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

risked estimates. For gas accumulations, all liquids are included in the NGL category. 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. Shading indicates not applicable]

Total petroleum system and assessment unit (AU) AU

probability

Accumulation 

type

Total undiscovered resources

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

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

Paleozoic–Mesozoic Composite Total Petroleum System

Wyoming Thrust Belt Conventional Oil and

Gas AU 1.0 Oil 7 21 66 26 18 52 166 66 2 5 17 7

Gas 244 574 1,231 634 13 34 77 38

Total undiscovered conventional resources 7 21 66 26 262 626 1,397 700 15 39 94 45

References Cited

Burtner, R.L.; and Nigrini, Andrew, 1994, Thermochronology of the 

Idaho–Wyoming Thrust Belt during the Sevier Orogeny—A new, 

calibrated, multiprocess thermal model: American Association of 

Petroleum Geologists Bulletin, v. 78, no. 10, p. 1586–1612.

Burtner, R.L.; Nigrini, Andrew; and Donelick, R.A., 1994, Thermochronology of Lower Cretaceous source rocks in the Idaho–Wyoming 

Thrust Belt: American Association of Petroleum Geologists Bulletin, 

v. 78, no. 10, p. 1613–1636.

Edman, J.D., and Surdam, R.C., 1984, Influence of overthrusting on 

maturation of hydrocarbons in Phosphoria Formation, Wyoming–

Idaho–Utah Overthrust Belt: American Association of Petroleum 

Geologists Bulletin, v. 68, no. 11, p. 1803–1817.

Lamerson, P.R., 1982, The Fossil Basin and its relationship to the 

Absaroka thrust system, Wyoming and Utah, in Powers, R.B., ed., 

Geologic studies of the Cordilleran Thrust Belt, volume I: Denver, 

Colo., Rocky Mountain Association of Geologists, p. 279–340.

Lillis, P.G.; and Selby, David, 2013, Evaluation of the rhenium–osmium 

geochronometer in the Phosphoria petroleum system, Bighorn Basin 

of Wyoming and Montana, USA: Geochimica et Cosmochimica 

Acta, v. 118, p. 312–330.

Maughan, E.K., 1984, Geologic setting and some geochemistry of 

petroleum source rocks in the Permian Phosphoria Formation, in

Woodward, Jane; Meissner, F.F., and Clayton, J.L., eds., Hydrocarbon source rocks of the Greater Rocky Mountain region: Denver, 

Colo., Rocky Mountain Association of Geologists, p. 281–294.

Warner, M.A., 1982, Source and time of generation of hydrocarbons in 

the Fossil Basin, western Wyoming Thrust Belt, in Powers, R.B., ed., 

Geologic studies of the Cordilleran Thrust Belt, volume II: Denver, 

Colo., Rocky Mountain Association of Geologists, p. 805–815.

Webel, Suzanne, 1987, Significance of backthrusting in the Rocky 

Mountain Thrust Belt, in Miller, W.R., ed., The thrust belt revisited: 

Jackson Hole, Wyoming Geological Association, 38th Annual Field 

Conference, Guidebook, p. 37–53.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered 

conventional oil and gas resources within the Wyoming 

Thrust Belt Province (table 2). The estimated mean totals 

for undiscovered oil and gas resources are 26 million barrels 

of oil (MMBO) with an F95–F5 range from 7 to 66 MMBO, 

700 billion cubic feet of gas (BCFG) with an F95–F5 range 

from 262 to 1,397 BCFG, and 45 million barrels of natural 

gas liquids (MMBNGL) with an F95–F5 range from 15 to 

94 MMBNGL.