Large accumulations of gas containing high percentages of naturally occurring subsurface carbon dioxide are located in several geographic provinces of the United States. Central Mississippi, West Virginia, the Delaware--Val Verde Basins of West Texas and several locations in the Rocky Mountains contain gas deposits with high percentages of carbon dioxide. Preliminary characterizations of reservoir rock quality and gas composition were performed for these areas. Four significant accumulations of carbon dioxide were chosen for in-depth geologic, reservoir, and economic analyses. Anticipated flowing pressure, sustained flow rates, recovery efficiencies, original gas in place, and reserves were determined. Sensitivity studies designed to bracket a possible range of prices were generated, utilizing estimated development and production costs, for each of the four areas. Projections of the potential supply, profitability of drilling and producing, and preliminary analysis of potential demand for naturally occurring carbon dioxide are presented.