Shales are sedimentary rocks that have a relatively high content of a bituminous substance called kerogen and 30% - 60% organic matter and fixed carbon. Kerogen, although not a definite chemical compound, yields an oily substance when heated (retorted) in the absence of air.
Oil shale is a light brown to black shale that contains hydrocarbons in the form of waxy spores and pollen grains. Under proper treatment these hydrocarbons can be distilled and used to prepare petroleum products.
Extraction of oil shale with ordinary solvents produces no oil, and their solubility in solvents is low.
The oils derived from oil shales are not true petroleum, although they are petroleumlike after being subjected to specialized chemical processing.
Most of the world's known unconventional oil resources are located in North America. Some 1.7 trillion barrels of oil are contained in the oil sands of Canada. An additional 2.0 trillion barrels are contained in oil shale located in Colorado, Utah, Wyoming, Kentucky, Ohio, and Indiana.
The largest reserves of oil shale in the world occur in the Eocene Green River Formation of the wesern United States [ CO-WY ]. The petroleum that can be distilled readily from the minable beds of oil shale of the Green River Formation (that is, those yielding 30-35 gallons per ton, 125-150 liters per ton) have been estimated as 160 billion barrels.
The shale that seals the bald-headed structures in much of KS is the Cherokee Formation (of Atoka-Des Moines age). This shale contains long, thin lenses of sand called "shoe-string sands." Most of the Cherokee sands are believed to have been channel fillings. They form the reservoirs for several productive oilfields in KS.