The classification of kerogen according to its chemical composition and its visual properties. Based on C, H, O, N, and S compositions, four basic types are defined: I, II, III, and IV. Type I and II kerogen produce oil when the kerogen has matured and gas when post-mature; Type III kerogen produces gas after being subjected to significant thermal maturity. Type IV is an inert kerogen. A Type IIS kerogen is from a sulfur rich kerogen that decomposes into heavier, sulfur rich oil at somewhat lower thermal maturity.
See Type I kerogen, Type II kerogen, Type III kerogen, Type IV kerogen, and Type IIS kerogen.