The solubilities of nitrogen and carbon dioxide in polystyrene were measured by a pressure decaying method at temperatures from 373.2 K to 453.2 K and pressures up to 20 MPa. The isothermal solubilities of both gases increase almost linearly with pressure. The solubility of carbon dioxide decreases with increasing temperature. The solubility of nitrogen, however, increases with temperature, and is about 1/16 to 1/7 of that of carbon dioxide. The solubilities measured are correlated by the Sanchez-Lacombe equation of state using the characteristic parameters for nitrogen and carbon dioxide determined in our previous work. The parameters for polystyrene were determined using the experimental PVT data measured in our laboratory. Agreement between the experimental solubilities and the correlations with a temperature-dependent binary interaction parameter, k(ij), is satisfactory. Henry’s constants for carbon dioxide + and nitrogen + polystyrene systems are in relatively good agreement with Durill’s data.