Optimization of oil preparation apparatus parameters is significant for designing and exploitation of oil and gas equipment. Furthermore, the effective predicting of separation mechanisms accompanied by phase transformation and structural instability of component composition and thermal properties is important. Theoretical approach in this problem is extremely actual, valuable and practically significant due to the absence of experimental data. The main aim of the study is to determine the regularities of multicomponent hydrocarbon media evolution in separation modes in oil preparation apparatus: the temperature is T?0…70 °C and pressure is P?0,1…3,5 MPa. The methods: thermodynamic models in HYSYS software such as Peng-Robinson equation of state, Lee-Kesler-Plocker equation of state, NRTL equation, Grayson-Streed semi;empirical model; similarity theory. The results. The paper introduces the data on the features of changes in similarity criteria in gaseous continuous media characterizing heat, mass and impulse transfer. The authors have studied the features of changes in composition and thermal properties of gas mixture depending on temperature and pressure of oil preparation apparatus. It was determined that the data of calculation of criteria change are successful for predicting the processes in real gases. It was noted that calculation values of Prandtl, Schmidt and Lewis numbers for one component chemically homogeneous systems are correlated well enough with the experimental information. The discussed mathematical model for determining the transfer parameters can be verified by the data of the experimental study of self; diffusion phenomena.