This paper describes a method for predicting constants in the equation of state (EOS) for saturated and compressed refrigerant fluids from analysis of speed of sound results and using two scaling constants. The theoretical EOS is that of Song and Mason, which is based on statistical-mechanical perturbation theory, and the two constants are enthalpy of vaporization DeltaH(vap) and molar density rho(nb), both at the normal boiling temperature. The following three temperature-dependent quantities are required to use the EOS: the second virial coefficient B-2(T), an effective van der Waals covolume, b(T), and a correction factor, alpha(T). The second virial coefficients are calculated from a two-parameter corresponding states correlation, which is obtained from a speed of sound data analysis with the two constants DeltaH(vap) and rho(nb) as scaling parameters. b(T) and alpha(T) can also be calculated from second virial coefficients by scaling rules. This EOS is applied to six refrigerants: 1,1-dichloro-2,2,2-trifluoroethane (R123), 1,1,1,2-tetrafluoroethane (R134a), 1,1-dichloro-1-fluoroethane (R141b), 1,1-difluoroethane (R152a), chlorodifluoromethane (R22), and difluoromethane (1132). The results show that the liquidlike densities of these refrigerants at the temperature range 0.8T(nb) < T < 1.1T(c) can be predicted to within 3%.