The major challenges facing fuel cells in light-duty vehicle applications relate to the high cost of the fuel cell stack components (membrane, electro-catalyst and bipolar plate) which dictate that new manufacturing processes and materials must be developed. initially, the best fuel for a mass market light-duty vehicle will probably not be the best fuel for the fuel cell (hydrogen); refueling infrastructure and energy density concerns may demand the use of an on-board fuel processor for petroleum-based fuels since this will increase customer acceptance. The use of fuel processors does, however, reduce the fuel cell system's efficiency. Moreover, if such fuels are used then the emissions benefit associated with fuel cells may come with a significant penalty in terms of added complexity, weight, size and cost. However, ultimately, fuel cells powered by hydrogen do promise to be the most efficient and cleanest of automotive powertrains.