The design and construction of a test facility and methodology for measuring the solubility and viscosity of lubricating oil/refrigerant mixtures at high pressures and temperatures are described. An auxiliary charging system, developed to provide precisely measured quantities of oil and refrigerant to the test facility, is also presented. The test facility was developed under the sponsorship and supervision of ASHRAE which funded this research project (RP-580);The solubility, viscosity and density of mixtures of R-22 and of R-502 with commonly used 150 SUS lubricants have been measured by using this facility. Specifically, results for liquid mixtures of 10% to 40% refrigerant (by mass) in a 150 SUS naphthenic oil and in a 150 SUS alkylbenzene are reported over the temperature range of 100°F (38°C) to 300°F (149°C). The oil/refrigerant mixtures for R-22 were miscible over the complete range tested, while for the R-502/naphthenic oil mixtures, two coexistent liquid phases were encountered in tests at the higher refrigerant concentrations;The property test results are presented in graphical form as well as in the form of empirical correlations based on a nonlinear regression analysis of the experimental data. Comparisons with the limited data previously published in the open literature show reasonable agreement.