Coal is the most abundant energy source in the world, and it is a major source of hydrocarbons, particularly gas. The coalification process, whereby plant material is progressively converted to coal, generates large quantities of methane-rich gas, which are stored within the coal. The presence of this gas has been long recognized due to explosions and outbursts associated with underground coal mining. Only recently has coal been recognized as a reservoir rock as well as a source rock, thus representing an enormous undeveloped "unconventional" energy resource. But production of coalbed methane (CBM) is accompanied by significant technical and environmental challenges, including disposal of large quantities of water produced with the gas. CBM production was initially spurred by a tax incentive. Internal Revenue Code Section 29 provided a non-refundable tax credit for sale of CBM (as well as other qualified alternative fuels) from wells drilled between 1980 and 1992 inclusive, for sales of fuel between 1980 and 2002 inclusive.