Coalbeds are both source and reservoir rocks for major quantities of natural gas. Large amounts of natural gas are generated in coalbeds throughout their burial history by both biogenic and thermogenic processes. Coalbed gases are variable in their molecular and isotopic composition. In addition to methane, they can contain significant amounts of heavier hydrocarbons and CO[sub 2]. The primary controls of hydrocarbon gas composition are coal rank and composition, and depth/temperature. Coalbed gas is stored (sorbed) upon and within the molecular structure of the coal. As a result, coal has the ability to hold much more gas than the same rock volume of a conventional reservoir in gas occurs as a free or dissolved phase. The amount of gas stored is a function of rank, pressure, and temperature. Matrix permeability is essentially nonexistent in coal and flow pathways for gas are provided by the fracture (cleat) system. Regardless of rank, nearly all coals contain at least some water (inherent moisture, meteoric, and (or) from adjacent aquifers). Economic quantities of natural gas can be produced from coalbed reservoirs; desorption results from dewatering and subsequent depressurization of the coalbeds. The main environmental concerns about coalbed gas extraction are related to (1) methanemore » emissions from coal mining and (2) disposal of produced water. However, significant amounts of methane can be captured prior to and during mining, and the water produced can be disposed of in an environmentally acceptable manner, such as in injection wells. Estimated resources of coalbed gas are enormous and widely distributed around the world. However, this resource is essentially undeveloped, except in the United States where some production and technological advances have taken place. 60 refs., 13 figs., 2 tabs.« less