The representation of solubility isotherms of gases and vapors in glassy polymers has been analyzed through the use of a thermodynamic model, nonequilibrium lattice fluid, recently introduced. The possible use of the model as a predictive tool for gas solubility in glassy polymers has been discussed in previous works for the special cases in which the polymer density in pseudoequilibrium conditions is known from experimental measurements. In this paper, a different use of the model is presented in which the polymer density at different sorption conditions is not known from direct experimental measurements and is thus treated as a correlation parameter, following the typical linear dilation isotherm. The solubility isotherms thus obtained by the model have been compared with several experimental data, obtaining a rather satisfactory representation of the sorption isotherms, through use of two fitting parameters, at most.