There are no reserves of oil shale in the United States because one must have demonstrated commercial production in order to book reserves of oil. In 2010, the USGS upped Colorado's oil shale resources
to ~1.53 trillion barrels of potentially recoverable oil in the Piceance Basin. Whereas this seems like a huge number (and it is), a major question is at what rate it can be produced. To view a summary of the USGS report on the Piceance resources, click here
The out-of-date graph below shows the magnitude of Colorado's oil shale resources because virtually all of U.S. resources in this study were in Colorado.