The sorption of C-2 and C-3 hydrocarbons in two ethylene-propylene copolymers and a propylene homopolymer and the simultaneous dilation of the polymers were measured at temperatures of 287-363 K and pressures up to 4 MPa. The sorption isotherms were well described by the Flory-Huggins theory of dissolution. Dilation isotherms in the form of elongation versus pressure were similar in shape to the corresponding sorption isotherms. Solubility coefficients, partial molar volumes, and Flory-Huggins interaction parameters were determined from these isotherms. The thermal expansivities of the hydrocarbons dissolved in the polymers were 0.002-0.005 K-1, and the Flory-Huggins interaction parameters depended not only on temperature but also on concentration. At 323 K, the calculated solubilities of propylene in the ethylene-propylene-rubber regions of the copolymers were 1.8 times higher than in the amorphous regions of the propylene homopolymer.