Successful application of the reaction ensemble Monte Carlo (REMC) method to compute multiple-reaction chemical equilibria requires a reasonably high acceptance probability for all forward and backward reaction moves during the production stage of a simulation run. To achieve this for a system that involves almost irreversible multiple reactions. it is necessary to choose a thermodynamically-equivalent alternative set of linearly independent reactions. such that the occurrence of very large chemical equilibrium constants is avoided for as many reactions in the set as possible. In this work. the need for such a strategy is justified and applied to the combined hydrogenation of ethylene and propylene, which involves six components and requires a set of four linearly independent reactions. Already validated effective pair potential models were used: one-center Lennard-Jones (1CLJ) models for hydrogen and methane, two-center U plus point quadrupole (2CLJQ) models for ethylene, ethane and propylene, and a three-center LJ (3CLJ) model for propane. No binary adjustable parameters were needed to compute the unlike-pair U interactions. Simulation results were obtained for the effect of temperature and pressure on the conversions of ethylene and propylene, yield of methane, and density of the system at equilibrium. These results were found to be in very good agreement with calculations using the PSRK group contribution equation of state. (c) 2006 Elsevier B.V. All rights reserved.