The Frio Fluvial-Deltaic Sandstone (Vicksburg Fault Zone) play of South Texas has produced nearly 1 billion barrels (Bbbl) of oil since field development began in the 1940's. More than half of the reservoirs in this depositionally complex play have been abandoned, although large volumes of oil remain.

Five coal basins in the Rocky Mountain Foreland of the western United States--San Juan, Greater Green River, Piceance, Powder River, and Raton--contain, by virtue of their tremendous coal tonnage, 522 Tcf (14.7 Tm3) coalbed gas resources, or 77 percent of the nation's total of 675 Tcf (19.1 Tm3), and each is attractive in terms of coalbed methane exploration and development. Only in the San Juan Basin (84 Tcf; 2.38 Tm3), however, are these coalbed resources being extensively exploited to meet the nation's demand for natural gas.