The swelling of glassy polymers (PMMA and PS) due to CO2 sorption, under high pressures and relatively high temperatures, was investigated. Two experimental methods were used: the magnetic Suspension balance (MSB) and the optical determination of the volume change. The MSB measurements, in combination with previously reported sorption data obtained by the mass-loss analysis (MLA) and quartz-crystal microbalance (QCM) methods, provided a new way of determining the sorption-induced polymer swelling, which is especially important at high pressures. The Non-Random Hydrogen-Bonding (NRHB) model of mixtures of fluids was used to correlate the swelling data at all investigated conditions. The model was modified in order to be applicable to non-equilibrium conditions and was used to correlate the swelling at the glassy state. Whenever possible, the swelling isotherms were compared with the corresponding isotherms from the literature. In general, there is a good agreement between our experimental measurements and the literature ones. This proves, in particular, the complementary character of the MLA and MSB methods for the measurement of swelling of polymers at high pressures and temperatures and the satisfactory theoretical prediction by the NRHB and the Non-Equilibrium NRHB model of swelling in the rubbery and the glassy state, respectively. (C) 2006 Elsevier B.V. All rights reserved.