Abstract Shale gas is produced from the Woodford, Caney, and Fayetteville shales (Devonian and/or Mississippian), and coal-bed gas is produced from the Hartshorne and McAlester coal beds in the Arkoma basin of Oklahoma and Arkansas. The U.S. Geological Survey is currently assessing the technically recoverable hydrocarbon resources of the Arkoma basin and for assessment purposes has divided the continuous shale gas (unconventional) resources into three total petroleum systems together with their associated assessment units (AUs). Each of the gas shale AUs contains 2.5 % or more total organic carbon, is thermally mature with respect to gas generation over much of its area within the basin, and may be accessed by the drill at depths less than 14,000 feet. In addition, the Woodford, Caney, and Fayetteville Shale Gas AUs underlie relatively large areas that have not been tested adequately by the drill. Coal-bed gas is currently being produced from the Hartshorne and McAlester coal beds in the Arkoma basin, and for assessment purposes they have been grouped together into one total petroleum system and one AU. Much of the area where the coal beds are relatively shallow in the northern part of the AU has been drilled. However, the area underlain by coal in the southern part of the basin, which is deeper and more structurally deformed, remains largely unexplored for coalbed methane.