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 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 coalbed 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.