Fuel-processing is a bridging technology to assist the commercialization of fuel cell systems in the absence of a hydrogen infrastructure. The Argonne National Laboratory has been developing fuel-processing technologies for fuel cells, and has reported the development of novel catalysts that are active and selective for hydrocarbon-reforming reactions. It has been realized, however, that with pellets or conventional honeycomb catalysts, the reforming process is mass-transport limited. This study addresses the development of catalysts structures with microchannels that are able to reduce the diffusion resistance and, thereby, achieve the same production rate within a smaller reactor bed. The microchannel reforming catalysts are prepared and tested with natural gas and gasoline-type fuels in a microreactor (diameter: 1 cm) at space velocities of up to 250 000 h(-1). The catalysts have also been used in engineering-scale reactors (10 kWe; diameter: 7 cm) with similar product qualities. Compared with pellet catalysts, the microchannel catalysts offer a nearly five-fold reduction in catalyst weight and volume. (C) 2004 Published by Elsevier B.V.