Autothermal reforming (ATR) has several advantages for fuel cell applications, such as a compact reactor structure and fast response. Using oxidation reactions inside the reactor, ATR does not have the external heat transfer limitations associated with steam reforming. However, mass and heat transfer limitations inside and outside the catalyst particles are still anticipated. In this study, transport limitations in the steam reforming section of ATR over a Pt/Gd-doped ceria catalyst are analyzed by numerical simulations based on a reaction rate equation in which parameters are adjusted to measured kinetic data. The simulation results show that significant transport limitations characterize the steam reforming section of packed-bed ATR reactors. The activity per catalyst bed volume is highly dependent on the particle size, and only the thin exterior layer of the particles is involved in catalyzing the reactions. Based on the results, it is shown that an eggshell type catalyst particle could reduce catalyst material significantly without a considerable decline in the activity per catalyst bed volume. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.