The kinetics of CO preferential oxidation (PROX) was studied to evaluate various rate expressions and to simulate the performance the CO oxidation step of a methanol fuel processor for fuel cell applications. The reaction was carried out in a micro reactor testing unit using a commercial Engelhard Selectoxo (Pt-Fe/gamma-alumina) catalyst and three self-prepared catalysts. Temperature was varied between 100 and 300 degreesC, and a of range feed rates and compositions were tested. A reaction model in which three reactions (CO oxidation, H-2 oxidation and the water gas shift reaction) occur simultaneously was chosen to predict the reactor performance. Using non-linear least squares, empirical power-law type rate expressions were found to fit the experimental data. It was critical to include all three reactions to determine good fitting results. In particular, the reverse water gas shift reaction had an important role when fitting the experimental data precisely and explained the selectivity decrease at higher reaction temperatures. Using this three reaction model, several simulation studies for a commercial PROX reactor were performed. In these simulations, the effect of O-2/CO ratio, the effect of water addition, and various non-isothermal modes of operation were evaluated. The results of the simulation were compared with corresponding experimental data and shows good agreement. (C) 2003 Published by Elsevier B.V.