Fuel cells have high efficiency for conversion of fuel to electricity. However, most types of fuel cells do not have high power density and efficiency operating directly from existing hydrocarbon fuels, thus require fuel reforming. Fuels are likely to be different for differing fuel cell applications, and debates exist about future fuels for fuel cell transportation applications. Potential on-board vehicle applications for fuel cells include both prime mobility power and auxiliary power production.This work examines fuel reforming for PEM fuel cells for prime mobility for transportation applications. Major gasoline and diesel fuel constituents, such as aliphatic compounds, napthanes, and aromatics have been compared for their effect on the fuel processing performance, and fuel processor catalyst requirements. Hydrogen production from the catalytic oxidation and steam reforming of liquid hydrocarbon fuels is compared with homogeneous oxidation and catalytic steam reforming. Fuel processing performance of individual components is compared with the fuel processing performance of blended fuel components and reformulated gasoline to examine synergistic or detrimental effects the fuel components have in a real fuel blend.