A model of continuous-site distribution for gas sorption in glassy polymers is examined with sorption data of CO2 and Ar in polycarbonate. A procedure is presented for determining from a measured isotherm the number of sorption sites in a polymer, an important parameter that previously had to be assumed. With this parameter value and solubility data obtained at zero pressure, the model can reasonably predict sorption isotherms of CO2 in glassy polycarbonate for a wide temperature range. The number of sorption sites and the average site volume evaluated from CO2 sorption isotherms are employed for the prediction of Ar sorption isotherms with zero-pressure solubility data and the independently measured partial molar volume of Ar. A reasonable fit to the measured isotherms of Ar is achieved. With the proposed procedure, the continuous-site model shows several advantages over the conventional dual-mode sorption model.