The kinetics of the CO desorption process have been determined using isotopic exchange experiments at concentrations and temperatures relevant to PEM fuel cells operating with reformate gas and commercial carbon supported platinum-ruthenium alloy anodes. The CO desorption kinetics have been studied as a function of CO concentration, temperature and flow rate. Desorption rate constants have been determined experimentally for a wide range of concentrations (100-500 ppm) and temperatures (25-150 degrees C) and have been extrapolated to one order of magnitude lower CO concentration range between 10 and 100 ppm, which is directly relevant to PEM fuel cells operating with reformate gas. The desorption rates measured for the 100-500 ppm CO concentration range appear to be significantly larger than previously published CO oxidation data, suggesting that the CO desorption process plays a more significant role in determining the equilibrium CO coverage at the fuel cell anode than the electrochemical CO oxidation process. The proposed desorption rate values at the lower 10-100 ppm CO concentration range and at relevant temperatures are believed to be of added value for the modelling of PEM fuel cells operating with reformate gas and PtRu/C anodes, since significantly different empirical values have been used up to now for the modelling of the CO desorption process. The variation of the apparent Arrhenius parameters as a function of CO concentration provides also some insight into the CO poisoning effect and the underlying adsorption/desorption processes. (c) 2009 Elsevier B.V. All rights reserved.