The sorption and swelling of polystyrene, poly(methyl methacrylate), poly(vinyl pyridine) and polyisoprene, and of styrene-methyl methacrylate, styrene-vinyl pyridine and styrene-isoprene block copolymers, in the presence of carbon dioxide, is examined at 35 degrees C and at pressures to 1500 psia. Sorption data were obtained using a quartz spring technique and swelling data were obtained by direct measurement of the dimensions of a separate sample using a cathetometer. Sorption in the glassy polymers increases linearly at low pressures before leveling off at higher pressures, while sorption in the rubber polyisoprene is linear over the entire range of pressures investigated. Sorption in the block copolymers shows a continuous transition from the behavior of one homopolymer to the behavior of the other. The Sanchez-Lacombe equation of state is used to model the homopolymer data using the concept of order parameters to extend the model to the glassy polymers. A simple linear model based on the homopolymer sorption is adequate to describe the copolymer results.