Oil shale is a rock that contains significant amounts of organic material in the form of kerogen. Up to 1/3 of the rock can be solid kerogen. Liquid and gaseous hydrocarbons can be extracted from oil shale, but the rock must be heated and/or treated with solvents. This is usually much less efficient than drilling rocks that will yield oil or gas directly into a well. Extracting the hydrocarbons from oil shale produces emissions and waste products that cause significant environmental concerns. This is one reason why the world’s extensive oil shale deposits have not been aggressively utilized.

Oil shale usually meets the definition of “shale” in that it is “a laminated rock consisting of at least 67% clay minerals.” However, it sometimes contains enough organic material and carbonate minerals that clay minerals account for less than 67% of the rock.