A molecular-based Monte Carlo computer simulation method is presented for modeling vapor-compression refrigeration cycles involving an arbitrary working fluid. It can be used to predict cycle properties, requiring only knowledge of the chemical composition of the working fluid. The approach can thus be used for preliminary design considerations for alternative refrigerants in the absence of available experimental and/or accurate equation-of-state data. The method calculates the properties of the working fluid at the states of the cycle, and the resulting coefficient of performance. The approach is based on the combination of appropriate molecular-level simulation techniques to model each process of the cycle. It employs a molecular-level model of the species of the working fluid, which is typically readily constructed from available molecular force-field models. Example calculations are shown for two common refrigerants, and compared with the results of equation-of-state calculations. (C) 2007 Published by Elsevier B.V.