Published estimates of the U.S. potential gas resource base vary considerably in magnitude. However, one finds a general agreement that a large, accessible natural gas resource base exists that both backs up the current inventory of proved gas reserves and is available to make a larger contribution to the nation’s energy supply. From a comparison of six such estimates by four industry and government organizations, this paper attempts to facilitate understanding of the differences in their (1) perceptions of the resource base, (2) data sources, and (3) analytical approaches. These differences lead directly to the differences in reported results. The apparent magnitudes of these differences diminish, however, on examination of the assumptions made by the organizations (particularly concerning the role of technology) and how they have defined the categories of assessed gas resources.