Solid polymer fuel cells (SPFCs) are attractive as electrical power plants for vehicle applications since they offer the advantages of high efficiency, zero emissions, and mechanical robustness. Hydrogen is the ideal fuel, but is currently disadvantaged for automotive applications by the lack of refuelling infrastructure, bulky on-board storage, and safety concerns. On-board methanol reforming offers an attractive alternative due to its increased energy storage density. Since CO is always present as a by-product during the reforming reaction, it must be reduced to a level less than 20 ppm in order to avoid rapid deactivation of the platinum electro-catalyst in the fuel. cells. In this paper a compact CO selective oxidation unit based upon two coated aluminium heat exchangers, developed at Loughborough University, is reported. The geometric size of the whole unit is 4 litre and experimental results show that the selective oxidation unit can reduce the CO from up to 2% to less than 15 ppm and is suitable far a vehicle fuel cell power plant of 20 kW(e).