A methanol fuelled P.E.M. fuel cell power plant with a baseline output of 112 kW (150 HP) was simulated using previously developed models for the various sub-systems. The duty cycle of a typical tractor-trailer for long distance haulage was used as the design basis. The integration of the various components of the system was examined in detail. By recovering heat from the fuel cell cooling system, burning excess hydrogen from the fuel cell anode exhaust and thermally coupling the exothermic selective oxidizer with the endothermic methanol steam reformer, the fuel supply sub-system can be made autothermal (ie.requiring no additional heating). Utilizing turbochargers on the fuel supply sub-system and also on the final system exhaust significantly reduces the parasitic load required for compressing air. Assuming conservative efficiencies for compressors, gas turbines and the traction motor gave overall system efficiencies in the range of 32-35% based on the lower heating value of methanol. The effects of a number of operating conditions on efficiency were explored at a baseline power of 112 kW. Air compressor power, cooling system heat load and steam to methanol ratio in the feed were found to be the most significant operating parameters.