Adsorption and desorption isotherms of CO2 on dried Argonne Premium coal samples were investigated. A small hysteresis was detected between the adsorption and desorption isotherms. The hysteresis was small or negligible for high rank coals but discernable for low rank coals. The isotherms were found to be rectilinear and to fit the conventional adsorption equations poorly. The rectilinear shape of the adsorption isotherms was related to the solubility of the CO2 in the coal and to coal swelling. Using an adsorption model that accounted for volumetric effects provided good agreement between the surface areas calculated from the high-pressure isotherms and the literature values obtained under traditional low-pressure conditions. Ignoring the volumetric effects resulted in estimated surface areas that were 40% larger for the higher-ranked coals and 60-100% larger for the lower-ranked coals. The heat of adsorption, after correcting for volumetric effects, was fairly constant (26+/-1 kJ/mol) regardless of rank. The adsorption capacity, average pore size, and volume effect for each of the Argonne coals were also estimated employing the same model. The model equation explicitly accounts for volumetric effects, attributable to the solubility of CO, in the organic matrix and the coal swelling, and estimates the actual adsorbed amount. (C) 2003 Elsevier Ltd. All rights reserved.