Considering that the U.S. now mines roughly 300 to 400 million tpy from the PRB, this reserve would last at least 75 years. The PRB contains the largest deposits of low-sulfur subbituminous coal in the world. This study is significant, however, because it illustrates that only a relatively small percentage of in-place coal resources are technically and economically recoverable.

“The United States is well-known for its rich endowment of coal resources and our in-place estimates bear that out,” said USGS Acting Director Suzette Kimball. “It’s important to note, however, the substantial difference between what is in-place and what is technically recoverable, let alone economic. This new basin-wide assessment provides that critical link for government and private managers to make informed decisions.”

The key to this study was taking advantage of the wealth of recently available geologic data from the interpretation of thousands of new drill logs from coal bed methane development in the PRB. More than 8,000 new drill holes were added to the original Gillette coalfield database alone. About 30,000 total data points were used in the entire PRB assessment. This geologic information interpreted from well information of the recent drilling provided an unprecedented level of data about the coal resources for the basin.

The USGS developed the geologic information that formed the basis of this assessment in cooperation with the Wyoming State Geological Survey and the Montana Bureau of Mines and Geology.

The basin was divided into four areas for assessment: the Montana Powder River Basin, the Northern Wyoming Powder River Basin, the Gillette coalfield and the Southwestern Wyoming Powder River Basin. Within these four areas, the USGS assessed coal resources for 47 coal beds. The three largest beds by resource are the Canyon coal bed, the Anderson coal bed and the Smith coal bed. These three coal beds together represent about 38% of the total coal resources for the PRB.