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The occurrence of [[natural gas]] in coal beds has been recognized for hundreds of years, because it is commonly released from the coal and occasionally causes deadly explosions in underground coal mines. [[Coal]] is the most abundant energy source in the Earth, and it should therefore be expected that large volumes of gas, generally called coalbed methane (CBM), should be present in coal deposits throughout the world, providing an enormous potential energy resource.<ref name=Bibleretal_1998>Bibler, C. J., J. S. Marshall, and R. C. Pilcher, 1998, [http://www.sciencedirect.com/science/article/pii/S0166516297000384 Status of worldwide coal mine methane emissions and use]: International Journal of Coal Geology, v. 35, nos. 1-4, p. 283-310.</ref>

The occurrence of [[natural gas]] in coal beds has been recognized for hundreds of years, because it is commonly released from the [[coal]] and occasionally causes deadly explosions in underground coal mines. [[Coal]] is the most abundant energy source in the Earth, and it should therefore be expected that large volumes of gas, generally called [[Coal bed methane|coalbed methane]] (CBM), should be present in coal deposits throughout the world, providing an enormous potential energy resource.<ref name=Bibleretal_1998>Bibler, C. J., J. S. Marshall, and R. C. Pilcher, 1998, [http://www.sciencedirect.com/science/article/pii/S0166516297000384 Status of worldwide coal mine methane emissions and use]: International Journal of Coal Geology, v. 35, nos. 1-4, p. 283-310.</ref>

Coalbed methane is generated during the coalification process, and most of it (98%) is found adsorbed in the coal, which is a [[microporous]] solid with large internal surface areas in the matrix pore structure that can adsorb very large amounts of gas. Lesser amounts can occur as free gas in [[fracture]]s (called [[cleat]]s) and large pores, and/or dissolved in the groundwater present in pores and fractures; coal serves as both the [[Source rock|source]] and the [[reservoir]] rock for the coalbed methane.

Coalbed methane is generated during the coalification process, and most of it (98%) is found adsorbed in the coal, which is a [[microporous]] solid with large internal surface areas in the matrix pore structure that can adsorb very large amounts of gas. Lesser amounts can occur as free gas in [[fracture]]s (called [[cleat]]s) and large pores, and/or dissolved in the groundwater present in pores and fractures; coal serves as both the [[Source rock|source]] and the [[reservoir]] rock for the coalbed methane.