U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3145

January 2013

In-Place Oil Shale Resources Examined by Grade in the 

Major Basins of the Green River Formation, Colorado,

Utah, and Wyoming

Oil shale in the Eocene Green River Formation—

including the Piceance Basin of northwestern Colorado, the 

Uinta Basin of northeastern Utah, and the Greater Green 

River Basin of southwestern Wyoming—is the world’s largest 

known deposit of kerogen-rich rocks (Dyni, 2006). The total 

potential resource within these deposits, regardless of grade, is 

estimated in the most recent U.S. Geological Survey resourcein-place assessment to be 4.285 trillion barrels of oil (Johnson 

and others, 2010 a, b; Johnson and others, 2011). Although 

this assessment is one of the most comprehensive of its kind, 

with a database of nearly a half million measurements made 

on samples collected throughout the three principal basins, it is 

only an assessment of resource-in-place and does not attempt to 

address the issue of how much of the resource is recoverable.

Figures 1, 2, and 3 show frequency and cumulative oil 

shale resource distributions as a function of grade for the three 

principal basins; the axes of all three figures are equivalent to 

facilitate visual comparison. Figure 4 combines all three basins 

in a complimentary cumulative distribution plot. The following 

overall values were determined for the entire Green River Formation: 1.146 trillion barrels (27 percent) of the total resource 

in the Green River Formation would be considered recoverable 

at a grade cutoff of 15 gallons of oil per ton of shale (GPT), and 

353 billion barrels (8 percent) would be considered recoverable 

at a grade cutoff of 25 GPT. Oil shale with this oil-generating 

potential (≥25 GPT) is often described as high grade. These 

values are similar to previous estimates of recoverable oil shale 

resources in the Green River Formation (Bartis and others, 

2005). Estimates of potentially viable (≥15 GPT) and highgrade (≥25 GPT) in-place oil shale resource for each basin are 

summarized in table 1.

It is important to put these values into context with respect 

to world crude oil reserves and domestic United States consumption levels. The most current estimate of world crude oil 

proved reserves by the U.S. Energy Information Administration 

(2012a) is 1.342 trillion barrels. Inclusion of high-grade Green 

River Formation oil shale resources (≥25 GPT) would increase 

this value by 26 percent, and adding all potentially viable oil 

shale (≥15 GPT) would nearly double it. At the current rate of 

oil consumption in the United States, which is roughly 19 million barrels per day (U.S. Energy Information Administration, 

2012b), high-grade Green River Formation oil shale resources 

represent a 50-year supply of oil. If the 15- to 25-GPT resource 

is included, then the prospective oil shale represents a 165-year 

supply of oil for the United States. By these measures, the oil 

shale of the Green River Formation represents an enormous 

potential resource.

Methods

The oil shale resource in the Green River Formation that 

is likely to be developed is expected to be limited to locations 

where high concentrations of high-grade oil shale are present. 

In some cases, lower-grade oil shale, yielding at least 15 GPT, 

may be potentially viable and therefore targeted or developed 

along with high-grade material. Oil shale grade is determined 

by the Fischer assay method, which is used to measure oil yield 

under a particular set of pyrolysis conditions (American Society 

for Testing and Materials, 1980). The first step in developing 

an estimate of the recoverable resource in Green River Formation oil shale deposits is to take the grade-dependent limitations 

for development into account. To that end, the distribution data 

relating oil shale grade (GPT) to total oil yield (barrels of oil) 

was extracted from the assessment database for the Piceance, 

Uinta, and Greater Green River Basins. Average grade was 

calculated on a per acre basis for each of the stratigraphically 

defined rich and lean zones identified in previous studies (Johnson and others, 2010 a, b; Johnson and others, 2011) throughout 

each of the three basins. These limits on the resolution of the 

analysis are consistent with the data density and stratigraphic 

resolution identified during the assessment. The total resource 

represented by each grade (0 to 50 GPT at 1 GPT increments) 

was summed to generate datasets of grade versus resource for 

each basin by zone. 

Using a geology-based assessment methodology, the U.S. Geological Survey estimated a total of 4.285 trillion 

barrels of oil in-place in the oil shale of the three principal basins of the Eocene Green River Formation. Using 

oil shale cutoffs of potentially viable (15 gallons per ton) and high grade (25 gallons per ton), it is estimated that 

between 353 billion and 1.146 trillion barrels of the in-place resource have a high potential for development.
Discussion

Comparing the overall grade distributions to those determined for individual intervals of the Green River Formation 

(data not shown) shows that the Mahogany zone oil shale 

represents the largest proportion of high-grade oil shale in the 

Piceance and Uinta Basins (108 billion and 1.3 billion barrels, respectively). Other notable zones in the Piceance Basin 

containing substantial amounts of high-grade oil shale resource 

are the R-4 (71.7 billion barrels), R-5 (61.3 billion barrels), and 

R-6 (36.5 billion barrels) zones, whereas in the Uinta Basin 

only the Mahogany zone represents any significant quantity of 

high-grade oil shale. None of the Greater Green River Basin 

zones contains any high-grade oil shale based on the analysis 

employed here, although it is known that some intervals within 

the rich zones contain high-grade material. 

A significant portion of the Green River Formation oil shale 

resource in the Piceance Basin (569 billion barrels) is potentially 

viable, falling between the 15- and 25-GPT cutoffs, and most is 

present in the R-1 (83.5 billion barrels), R-5 (71 billion barrels), R-6 (103 billion barrels), Mahogany (72.7 billion barrels), 

and Bed 44 (92.5 billion barrels) zones. All Piceance Basin rich 

zones, as well as some of the lean zones, contain significant 

resource that is potentially viable. In the Uinta Basin, only the 

Mahogany zone contains significant quantities of potentially 

viable oil shale. In the Greater Green River Basin, the Tipton 

Member of the Green River Formation contains 84 percent of the 

potentially viable oil shale in that basin.

Many technologies currently being developed are 

expected to be capable of exploiting leaner oil shale along with 

the high-grade material without incurring significant additional 

costs. Therefore, the values reported here should be viewed 

as conservative estimates. However, full recovery (defined as 

100 percent of oil yield determined by the Fischer assay) using 

some of the methods that are under development may not be 

achieved, in which case, this analysis overestimates the recoverable resource. It is also possible that measuring oil yield with 

the Fischer assay may not be the standard for resource recovery 

in the future. Some alternate approaches that use other criteria include (1) an estimate of total petroleum product (oil and 

hydrocarbon gases), (2) use of a weight or heating value basis, 

or (3) an assessment of energy return on investment using a 

thermodynamic analysis of the potential energy of the resource, 

the energy required to generate the products, and the energy 

generated by those products. 

Future work to further refine the estimate of recoverable 

oil shale resources in the Green River Formation will include 

analysis of how shale oil is likely to be produced based 

on technological limitations, particularly how much of the 

resource can be mined and utilized by surface-processing methods and how much can be developed through the application of 

in situ retorting technologies. At present, however, it is uncertain as to what level of oil shale development may ultimately 

be possible in the Green River Formation, given the many 

variables that bear on the question, or if significant development will ever occur. A 1- to 3-million-barrel-per-day industry 

may be a realistic scale for utilization of western United States 

oil shale resources over a period of a few decades (Bartis and 

others, 2005). However, issues of water usage and electricity 

needs are likely to be important limiting factors, along with a 

range of environmental concerns.

Figure 1. Oil shale resource in-place distribution plot for the Piceance 

Basin. The bars represent the total resource in the basin for a particular 

grade. The line represents the cumulative resource in place that 

includes all resource up to a particular grade. 

Figure 4. Complimentary cumulative distribution plot for the 

oil shale resource in-place in the principal basins of the Green 

River Formation. The basin distributions are stacked showing 

the overall distribution for the entire Green River Formation.

Figure 2. Oil shale resource in-place distribution plot for the Uinta 

Basin. The bars represent the total resource in the basin for a 

particular grade. The line represents the cumulative resource in place 

that includes all resource up to a particular grade.

Figure 3. Oil shale resource in-place distribution plot for the Greater 

Green River Basin. The bars represent the total resource in the basin 

for a particular grade. The line represents the cumulative resource in 

place that includes all resource up to a particular grade.

Total resource

in-place

Oil yield of 15 gallons per ton

(GPT) or greater

Oil yield of 25 gallons per ton

(GPT) or greater

Oil in-place As percent of total

in-place Oil in-place As percent of totalin-place

Piceance Basin 1,5251 920 60 352 23

Uinta Basin 1,3202 93.6 7 1.3 0.1

Greater Green River Basin 1,4403 133 9 -- 0

Total 4,285 1,146 27 353 8

Table 1. Oil shale resources in the principal basins of the Eocene Green River Formation.

[Resource figures are in billions of barrels; --, no resource meets criteria]

1

Johnson and others, 2010a.

2

Johnson and others, 2010b.

3

Johnson and others, 2011.
References Cited

American Society for Testing and Materials, 1980, ASTM 

D3904-90 Test method for oil from oil shale (resource evaluation by the Fischer assay procedure): West Conshohocken, 

Pa., American Society for Testing and Materials, Annual 

Book of ASTM Standards [withdrawn 1996].

Bartis, J.T., LaTourrette, Tom, Dixon, Lloyd, Peterson, D.J., 

and Cecchine, Gary, 2005, Oil shale development in the 

United States—Prospects and policy issues: Prepared by 

the Rand Corporation for the U.S. Department of Energy, 

National Energy Technology Laboratory, 68 p. 

Dyni, J.R., 2006. Geology and resources of some world oilshale deposits: U.S. Geological Survey Scientific Investigations Report 2005–5294, 42 p.

Johnson, R.C., Mercier, T.J., Brownfield, M.E., Pantea, M.P., 

and Self, J.G., 2010a, An assessment of in-place oil shale 

resources in the Green River Formation, Piceance Basin, 

Colorado, chapter 1 of Oil shale and nahcolite resources 

of the Piceance Basin, Colorado: U.S. Geological Survey 

Digital Data Series 69–Y, 187 p.

Johnson, R.C., Mercier, T.J., Brownfield, M.E., and Self, 

J.G., 2010b, Assessment of in-place oil shale resources in 

the Eocene Green River Formation, Uinta Basin, Utah and 

Colorado, chapter 1 of Oil shale resources of the Uinta Basin, 

Utah and Colorado: U.S. Geological Survey Digital Data 

Series 69–BB, 153 p.

Johnson, R.C., Mercier, T.J., Ryder, R.T., Brownfield, M.E., and 

Self, J.G., 2011, Assessment of in-place oil shale resources 

in the Eocene Green River Formation, Greater Green River 

Basin, Wyoming, Colorado, and Utah, chapter 1 of Oil shale 

resources of the Eocene Green River Formation, Greater 

Green River Basin, Wyoming, Colorado, and Utah: U.S. 

Geological Survey Digital Data Series 69–DD, 63 p.

U.S. Energy Information Administration, 2012a, International 

energy statistics—Proved reserves of oil and natural gas for 

the world [most recent estimates]: U.S. Energy Information 

Administration, Independent Statistics and Analysis, accessed 

June 28, 2012, at http://www.eia.gov/cfapps/ipdbproject/

iedindex3.cfm?tid=5&pid=57&aid=6&cid=ww,&syid=2008

&eyid=2012&unit=BB.

U.S. Energy Information Administration, 2012b, International 

energy statistics: U.S. Energy Information Administration, 

Independent Statistics and Analysis, accessed June 28, 

2012, at http://www.eia.gov/cfapps/ipdbproject/IEDIndex3.

cfm?tid=5&pid=54&aid=2.

By Justin E. Birdwell, Tracey J. Mercier,

Ronald C. Johnson, and Michael E. Brownfield

U.S. Geological Survey

Denver Federal Center

Box 25046, MS 977

Denver, CO 80225

Photographs. Left: View from Wilkins Peak near Rock Springs, 

Wyoming. Inside pages: Outcrop showing several rich and lean oil 

shale zones at the mouth of the Piceance Creek in Rio Blanco County, 

Colorado. Photographs by Ronald C. Johnson, U.S. Geological Survey.