The solubility parameter theory of Hildebrand and Scott extended for polymer blends originally has accounted for dissimilarities only between contact energies of the blend components, neglecting free volume effects which are predicted by the corresponding states theories. Biros et al., however, have shown that using expressions of the Prigogine-Flory corresponding state theories for energy and volume, effects of free volume will be implicitly included in the solubility parameter approach too. The results are similar then to those derived by the corresponding state theories. In addition, it is shown that in this case the temperature and pressure dependencies of the solubility parameters are predicted qualitatively correct. We performed this procedure with the Sanchez-Lacombe EOS theory instead of the Prigogine-Flory approach. Formally, identical expressions result, and the calculated solubility parameters evaluated according to the two EOS theories are in good agreement. However, because Sanchez-Lacombe’s approach is not a corresponding state theory, it is able to predict additionally qualitatively correct the dependence of the solubility parameters on chain length.