The recent nonequilibrium approach of Doghieri and Sarti for the solubility of gases in glassy polymers is reexamined. Analytical expressions for the equilibrium and nonequilibrium contributions to the chemical potential of the penetrant are presented. Volume dilation of the glassy matrix is explicitly taken into consideration. The role of the apparent partial molar or specific volume of the sorbed gas is also examined. The model is tested against the experimental data of Fleming and Koros for the solubility of CO2 in Bisphenol A polycarbonate.