The feasibility of fuel cell vehicles has now been verified by virtue of recent and ongoing field experience with both hydrogen and reformer based systems. The key issues regarding the timing and extent of fuel cell commercialization are becoming the ability to reduce costs to acceptable levels and the choice of fuel for the power system. The choice of fuel processing technology can dramatically influence the total power system. The design and development of a multi-fuel reformer/fuel cell system for transportation applications has been demonstrated using both software simulations and hardware demonstrations. Feasibility has been demonstrated through six years of prototype hardware and experimental testing culminating with the reformer and CO clean-up device being integrated with a PEM fuel cell. Recent efforts have focused on improving the performance of the various subsystems and increasing the power density and specific power of the integrated fuel processing subsystem. The results of the fuel processor and fuel cell integrated testing and the recent advances in subsystem performance are presented in this paper. Experimental studies were carried out to determine the effect of equivalence ratio, firing rate, and PROX performance on fuel cell performance and system efficiency. Performance in the reformer and CO clean-up tests were measured in terms of conversion efficiency (kWH2/kWfuel) and CO outlet concentration. Results of the reformer experiments show that conversion efficiencies ranging from 83-88% are achievable for California Phase II gasoline, ethanol, methanol and natural gas with CO exit concentrations of less than 1%. Steady-state PROX tests show exit CO concentrations of less than 10 ppm when operating at discrete points from 25% to 125% input power, and transient PROX tests show that step transients of 10-45 kWth in 2 seconds (17.5 kW/sec) are achievable.