A simple extension of cubic equations of state (EOS) to polymer systems has been proposed. The Soave-Redlich-Kwong (SRK) EOS was taken as a prototype to be used to describe the PVT behavior of polymer melts in a wide temperature and pressure range. Combined with a modified Huron-Vidal g(E)-mixing rule it was applied for modeling vapor-liquid equilibria of polymer-solvent solutions and the solubility of supercritical gases in polymer melts. Satisfactory results are obtained.