The U.S. state with the largest reserves of oil shale is Utah.

Utah holds the largest known oil shale reserves in the United States, primarily located in the Green River Formation, which spans parts of Utah, Wyoming, and Colorado. The state's reserves are estimated to contain trillions of barrels of oil equivalent, making it a key area for potential future oil shale production. While oil shale extraction is more costly and environmentally challenging than conventional oil production, Utah’s reserves continue to attract attention for their potential in meeting future energy demands.