Kerogen is the organic solid material that can generate oil and gas inside sedimentary rock.
It forms from the remains of organisms, including algae and plant material, that become buried in fine sediments. Over millions of years, increasing heat and pressure transform this organic matter into an insoluble substance dispersed through rocks such as shale.
During burial, kerogen passes through stages of thermal maturity. In the oil window, suitable kerogen can generate liquid petroleum; at greater maturity, it can generate natural gas. The exact products depend on the kerogen’s original organic material and chemical type.
Kerogen is not the same as bitumen. Kerogen is insoluble in ordinary organic solvents, while bitumen is soluble and represents mobile or extractable organic material. Oil shale contains kerogen, but it must be heated to release hydrocarbons because the kerogen has not naturally matured into flowing petroleum.