An in-depth review of published information concerning viscosities of oil-refrigerant solutions has been completed. Summaries are presented for solutions of R12, R22, R114, and R502 with a wide variety of mineral and synthetic oils. Very limited information is available at the higher temperatures of interest in some of the newer compressors. About 12 primary references are cited for both oil/Rl2 and oil/R22 mixtures, but only 3 significant studies have been reported for oil/R114 and 3 for oil/R502. Improved characterization of lubricants has been identified as an important requirement for future work. Correlation methods have had limited success in predicting viscosities of oil-refrigerant solutions. Comments and recommendations are offered concerning experimental methods and procedures for presenting viscosity data for these mixtures.