Gas solubilities and polymer swelling in propylene and semicrystalline polypropylene system at temperatures of 323.2 and 348.2 K and pressures up to propylene's vapor pressure were measured. Pressure, specific volume, and temperature (PVT) measurements of polypropylene were carried out at temperatures from 313 to 573 K and pressures up 200 MPa. Two kinds of polypropylenes, which had different stereoregularities, were used for both solubility and PVT measurements. The solubilities were correlated with the Sanchez-Lacombe equation of state (EOS) with temperature-dependent binary interaction parameters to within 5% average relative percentage deviation. Swelling ratios estimated with Sanchez-Lacombe EOS coupled with optimized interaction parameters were 20% lower than the experimental values.