Estimates of the in-place gas resources of the principal coal-bearing basins of the United States exceed 700 trillion cubic feet. Economically recoverable resources of coalbed gas are probably less than 100 Tcf. This represents about a 5-year supply at current U.S. consumption rates. The Appalachian, Black Warrior, and Illinois basins (shown in red) emit significant quantities of methane to the atmosphere as a result of underground mining.