Coalbed methane production occurs within an economically important and unique petroleum system. A petroleum system typically consists of a sedimentary basin that contains a hydrocarbon source rock and all of the oil and gas related to the source rock. The classical petroleum system consists of a hydrocarbon-generative shale source rock that, with burial and resultant heating, expulses oil and gas that are free to migrate to porous reservoir rock such as sandstone or limestone. A coalbed methane system is different in that the coal itself is both source and reservoir. The coal is a hydrocarbon source rock that evolved during burial heating into a substance similar in structure to activated carbon (an organic-based material that is chemically treated or heat-treated to markedly increase micropores, with a corresponding increase in the internal surface area and gas sorption capacity). The coal both produces methane gas and has the storage capacity to hold the gas in place. Migration outside the coalbed is unnecessary.