Steam reforming of methanol (CH3OH + H2O --> CO2 + 3H(2)) was studied over a commercial Cu/ZnO/Al2O3 catalyst for production of hydrogen onboard proton exchange membrane (PEM) fuel cell vehicles. A simple power-law rate expression was fitted to experimental data in order to predict the rates Of CO2 and H-2 formation under various reaction conditions. The apparent activation energy (E-a) was estimated to be 100.9 kJ mol(-1), in good agreement with values reported in the literature. Appreciable amounts of CO by-product were formed in the reforming process at low contact times and high methanol conversions. Being a catalyst poison that deactivates the electrocatalyst at the fuel cell anode at concentrations exceeding a few ppm, special attention was paid to the pathways for CO formation and strategies for its suppression. It was found that increasing the steam-methanol ratio effectively decreases CO formation. Likewise, addition of oxygen or air to the steam-methanol mixture minimises the production of CO. By shortening the contact time and lowering the maximum temperature in the reactor, CO production can be further decreased by suppressing the reverse water-gas shift reaction.