Convenient representations for the pressure, temperature, composition and viscosity of three refrigerant/lubricant mixtures are studied. Solubility results are obtained from different models for the activity of the mixtures and from application of thermodynamic perturbation theory.;Local composition models have the advantage that an approximate form for the temperature dependence of the activity is provided. This work provides an analysis of the applicability of local composition models based on Wilson's treatment of the Flory-Huggins approximation for the lattice gas model in which site-site interactions are neglected. We have presented a modification of the Wilson's approach in which site-site interactions in the lattice gas model are retained. We compare the accuracy of these local composition models with the simple Margules equation. The utility of the local composition approach is dependent upon the correctness of the assumed temperature dependence. The constants contained in these expressions can not be applied for prediction of the thermodynamic properties for which no experimental data is available. In contrast, group contribution methods are phrased in terms of parameters which are transferrable to other mixtures for which no thermodynamic property information exists. Here we consider the UNIFAC and evaluate the interaction parameters for R12/hydrocarbon and R22/hydrocarbon binary "groups".;Thermodynamic perturbation theory predicts pressure as a function of temperature and composition without requiring the calculation of the activity coefficients.;Well established methods given in the literature are used for the prediction of mixture viscosities and results are compared with the experimental data provided by the Refrigeration Laboratory at Iowa State University.