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Figure 1. The Eastern Great Basin Province (red line) of Nevada, Utah, Idaho, and Arizona. Shown 

are major thrust faults, teeth on upthrown side. 

National Assessment of Oil and Gas Fact Sheet

Assessment of Undiscovered Oil and Gas Resources

of the Eastern Great Basin Province, 2005

Introduction

The U.S. Geological Survey (USGS) recently 

completed an assessment of the undiscovered oil and 

gas potential of the Eastern Great Basin Province of 

eastern Nevada, western Utah, southeastern Idaho, 

and northwestern Arizona (fig. 1). The province 

includes Neogene basins, Neogene ranges and structures, the central Nevada thrust belt, and the Sevier 

thrust belt. The assessment was based on the primary 

geologic elements that constitute a total petroleum 

system (TPS): petroleum source rocks (source rock 

maturation, petroleum generation, and migration), 

reservoir rocks (based on sequence stratigraphy and 

petrophysical properties), and petroleum traps (formation and timing). Using this geologic framework, the 

USGS defined the Paleozoic-Tertiary Composite TPS 

and three assessment units (AU) within the TPS, and 

quantitatively estimated the undiscovered oil and gas 

resources within the three AUs (table 1).

Resource Summary

The USGS estimated a mean of 1.6 billion barrels 

of oil (BBO), a mean of 1.8 trillion cubic feet of gas 

(TCFG), and a mean of 85 million barrels of total natural gas liquids (MMBNGL) in the Paleozoic-Tertiary 

Composite TPS. All of the assessed undiscovered oil 

and gas resources are conventional (table 1).

Of the total mean 1.6 billion barrels of oil (BBO), 

a mean of 827 million barrels of oil (MMBO) is estimated to be in the Neogene Basins AU, a mean of 470 

MMBO in the Ranges and Other Structures AU, and a 

mean of 301 MMBO in the Sevier Thrust System AU.

Of the 1.8 TCFG, about 0.1 TCFG is estimated 

to be in the Neogene Basins AU, 1.2 TCFG in the 

Ranges and Other Structures AU, and 0.5 TCFG in 

the Sevier Thrust System AU.

Using a geology-based assessment 

methodology, the U.S. Geological 

Survey estimated a mean of 1.6 billion 

barrels of undiscovered oil and a mean 

of 1.8 trillion cubic feet of undiscovered 

natural gas in the Eastern Great Basin 

Province.

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS-2005-3053

May 2005 Printed on recycled paper

Printed on recycled paper
The range in estimates of undiscovered conventional oil and gas (table 1) reflects the uncertainty of assessing new field discoveries 

in the Eastern Great Basin Province. The small number of drilled wells and producing wells compared to the total geographic area of 

the province indicates a frontier (or unproven) status. The Neogene Basins AU has the best potential to add new reserves, with current 

production serving as a successful analogue. The Ranges and Other Structures AU is hypothetical with no current production. The recently 

discovered Covenant field in the Sevier Thrust System AU provides insight into the potential of that area.

Oil shale, coal-bed gas, and biogenic gas were not quantitatively assessed in this study.

For Further Information

Supporting geologic studies of total petroleum systems and assessment units and the methodology used in the Eastern Great Basin 

Province are in progress. Assessment results are available at the USGS Central Energy Team Web site: http://energy.cr.usgs.gov/oilgas/

noga/index.htm

Eastern Great Basin Assessment Team

Lawrence O. Anna (lanna@usgs.gov, 303.236.5451), Laura N.R. Roberts, Christopher J. Potter, Ronald R. Charpentier, Troy Cook, 

Timothy R. Klett, Richard M. Pollastro, and Christopher J. Schenk.

Table 1. Eastern Great Basin 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. 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]

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