Using a PVT apparatus for high pressure and temperature combined with a magnetic suspension balance, the solubility of carbon dioxide in linear and branched polypropylene (PP) was measured at temperatures from (453 to 493) K and at pressures of up to 31 MPa. The solubility of CO2 in both molten polymers increased linearly with pressure and decreased with temperature. However, above 20 MPa, the solubility-pressure relationship was no longer linear. This might be due to a significant hydrostatic effect on the swelling of the polymer that results from gas absorption above 20 MPa, so that swelling is no longer linearly related to pressure. At a high pressure, swelling significantly affects solubility, which is then no longer linearly related to pressure. It was noted that linear PP absorbs more gas than branched PP, due to the branched PP's chain entanglement. The solubility of CO2 in the PP melts was compared with semiempirical data (determined by empirically measuring gas uptake and theoretically predicting swelling) and theoretical values calculated from the Simha-Somcynsky (SS) and Sanchez-Lacombe (SL) equations of state (EOSs). The Simha-Somcynsky equation of state (SS-EOS) was observed to have a better prediction capacity of the swelling effect and to thus provide better solubility predictions for both semiempirical and theoretical cases than the Sanchez-Lacombe equation of state (SL-EOS).