The surface area and pore distributions of retorted Colorado oil shale were studied using nitrogen and carbon dioxide adsorption and mercury porosimetry. Shale surface area was studied as a function of the heating rate during retorting. Results were analyzed with the Langmuir; Brunauer, Emmett, and Teller; and Dubinin-Polanyi equations. It was found that surface area correlated well with the amount of residual organic carbon. Also, the surface areas determined with carbon dioxide were substantially larger than those determined with nitrogen. Duplicate samples were decharred by heating in air at 400/sup 0/C for 24 h. The surface areas of these samples were less than half of those with the residual carbon. The surface areas of the retorted and decharred samples were combined to obtain an estimate of the specific surface area of the residual organic carbon (typically 300 m/sup 2//g). Acid leaching of three samples from those above removed the carbonate minerals. The surface areas determined by carbon dioxide adsorption showed an increase by a factor of two to three over the unleached samples. This effect was attributed to the formation of a sponge like structure caused by the dissolution of micrometer-sized crystals of calcite and dolomite in the shale. The pore characteristics of the retorted shale was also examined by mercury porosimetry and nitrogen adsorption. Scanning electron microscope pictures demonstrate the origin of the porosity.