A new method for determination of the pseudocritical parameters has been developed which is based on adjustment of the pseudocritical parameters to the thermodynamic properties on the saturation line. Different sources of the methodological uncertainties in the investigation of thermodynamic properties for the refrigerant/oil solutions (ROS) have been examined. Requirements for the quality of the initial experimental data have been formulated. Calculated values of the pseudocritical parameters for compressor oils have been compared with the experimental data obtained by the method of pulse heating. It was shown that it is possible to determine the pseudocritical parameters of the ROS in the concentration range 0.3 less than or equal to omega(R) less than or equal to 1.0 within the framework of the theory of thermodynamic similarity. (C) 2003 Elsevier B.V. All rights reserved.