Extension of well established EoS for fluid mixtures to the description of thermodynamic properties of non-equilibrium glassy polymeric phases is considered and corresponding calculations for pseudo-equilibrium gas content are performed. Results obtained using three different "tangent hard spheres chain" EoS are discussed and compared with experimetnal data for low-pressure gas solubility in glassy polycarbonate. While the overall result allows to conclude that tools developed herein may be confidently used for pure predictions of gas and vapor solubility in polymeric material below the glass transition temperature, interesting differences among the performance of different models were observed which can be attibuted to the different form of interaction potential considered.