A recent theory based on the Simha-Somcynsky theory is applied to the solubility of the 1,1,1,2 tetrafluoroethane vapor in polystyrene. The requisite chemical potentials of the vapor and of its condensate in contact with the polymer involve the equations of state (eos) of the 3 species and are evaluated by means of literature information. Good agreement with experiment ensues at 120 degrees C and pressures up to 35 bar. At 90 degrees C systematic differences, increasing with pressure, result above 10 bar. These may be caused by the use of melt theory in the glass transition region and/or an inadequacy of the eos of the vapor at lower temperatures and elevated pressures. Extensions to further pairs, gaseous mixtures and the glassy state are indicated.