Oil shale is a general term applied to a fine-grained sedimentary rock containing significant traces of kerogen (a solid mixture of organic chemical compounds) that have not been buried for sufficient time to produce conventional fossil fuels. The name of oil shale is someway misleading as it needs not be shale, and the hydrocarbon in it is not oil. In addition to the oil shale, there are other groups of organic-rich sedimentary rock—bitumen-impregnated rocks (tar sands and petroleum reservoir rocks), and humic coals and carbonaceous shale.
The kerogen in oil shale can be converted to synthetic crude through the chemical process of pyrolysis. When heated to a sufficiently high temperature a vapor is driven off which can be distilled (retorted) to yield a petroleum-like shale oil—a form of non-conventional oil—and combustible shale gas. Oil shale can also be burnt directly as a low-grade fuel for power generation and heating, and be used as a raw material in the chemical and construction materials industries. Currently oil shales are used commercially for oil production in Estonia, Brazil and China, for power generation in Estonia, China, Israel and Germany, for cement production in Estonia, Germany and China, and for chemical industry in Estonia and Russia.
World deposits of oil shale are estimated to equal 2.9–3.3 trillion barrels of recoverable oil, 1.5–2.6 trillion barrels of which are in the United States. Attempts to develop these reserves, ongoing for over 150 years, have had limited success. Although still seen as a potential future alternative to conventional oil, world production reached a peak of 46 million tons in 1980 before falling to about 16 million tons in 2000 due to the high cost of production relative to conventional petroleum.
As the oil shale industry has number of environmental impacts, environmentalists have expressed concern over the extraction of shale oil, and protests appear to have contributed to the halting of the developing industry in Australia.