Ensuring efficient and reliable operation of reciprocating compressors in a wide range of operating parameters is one of the most important problems in design, manufacture and operation of compressor equipment. Reciprocating compressors, working as part of mobile automotive gas refuellers, are intended for compressing natural gas to a final pressure of 20–25 MPa. The task in designing such equipment is to determine the real properties of the compressible medium. We have carried out a theoretical study on the influence of initial gas parameters on the operation of the compressor. We have given the results for operation of the compressor both for compression of an ideal gas and for a real gas. The developed mathematical model and the method for determining the thermodynamic properties of methane have been briefly described, with the results of comparison of calculated and tabulated data given. The results of testing the mathematical model for adequacy have been presented.