Henry's law coefficients and partial molar volumes of 34 penetrants (5 inert gases, 6 inorganic gases, 17 hydrocarbon gases, 5 fluorinated gases, and CCl4 vapor) dissolved in poly(dimethylsilaxane) and low-density polyethylene were determined at 25 degrees C by measuring sorption of the gases and the concomitant dilation of the polymers. From the Henry's law coefficients and the partial molar volumes, Flory-Huggins parameters for polymer/gas interactions were estimated. The partial molar volumes were correlated with critical molar volumes of gases, and the interaction parameters were found to depend on the partial molar volumes. These relationships for the fluorinated gases were clearly different from those of all other gases. For CO2 and CH4 in poly(dimethylsiloxane), partial molar volumes and interaction parameters were obtained as a function of temperature over a range -30 to 95 degrees C. Thermal expansivities of these dissolved molecules were estimated to be 2 x 10(-3) degrees C-1 from the temperature dependence of partial molar volumes.