Fuel cell (FC) technologies are expected to become a viable solution for vehicular applications because they use alternative fuel converters and are environmentally friendly. However, a stand alone FC system may not be sufficient to satisfy the load demands, especially during cold start, peak demand periods or transient events, for vehicular applications. In addition, the FC system is not capable of being reversed for regenerative energy. An ultra-capacitor (UC) bank can supply a large burst of power but cannot store much energy. By operating the FC and UC in parallel, both steady state and peak power demands can be satisfied. Use of a FC/UC hybrid model provides a potential solution for better energy efficiency while reducing the cost of FC power technology. This paper describes a new modeling and design methodology for FC/UC hybrid vehicular power systems. A feasible design and a dynamic model have been presented for the proposed technique. Simulation results are presented, using the MATLAB, Simulink and SimPowerSystems environments, based on the mathematical and electrical models of the proposed system. (C) 2006 Elsevier Ltd. All rights reserved.