Oil-shale deposits are in many parts of the world. They range in age from Cambrian to Tertiary and were formed in a variety of marine, continental, and lacustrine depositional environments. The largest known deposit is in the Green River Formation in the western United States; it contains an estimated 213 billion tons of in-situ shale oil (about 1.5 trillion U.S. barrels).

Total resources of a selected group of oil shale deposits in 33 countries are estimated at 409 billion tons of in-situ shale oil, which is equivalent to 2.8 trillion U.S. barrels of shale oil. These amounts are very conservative because (1) several deposits mentioned herein have not been explored sufficiently to make accurate estimates, and (2) some deposits were not included in this survey.