Oil shale is an organic-rich fine-grained sedimentary rock formed on the bottom of lakes and seas 400–450 million years ago. Oil shale can be used directly as a fuel for producing energy or synthetic oil. Oil shale is not well known as a fuel for energy production, because it has been used much less than coal and crude oil.
Oil shale deposits are found in all world oil provinces, although most of them are too deep to be exploited economically. Well-explored deposits, potentially classifiable as reserves, include deposits in United States, Australia, Estonia, Jordan, Brazil, China, Mongolia and Russia.
Oil shale serves for oil production in Estonia, Brazil, and China; for power generation in Estonia and China; for cement production in Estonia, Germany, and China; and for use in chemical industries in Estonia and China.