Synthetic petroleum products recovered from western oil shale's are expected to play an important part in supplying energy needs to the United States during the later part of the 1900's. Various estimates of the magnitude of western oil shale reserves have been made. The U.S. Geological Survey estimates that an equivalent of about 4,000 billion barrels of oil are continued in the oil shale's of the Green River Formation of Utah, Colorado, and Wyoming. These oil shale resources account for 80 percent of the known world resources but, of course, are not completely recoverable. Recoverable resources are a function of mining and retorting technology and economics, but my amount to about 1,000 billion barrels o oil. As the estimated remaining world ultimate oil resources are about 2,000 billion barrels, of which less than 150 billion barrels are in the United States, western oil shale is clearly a significant energy resource.