Microchanneled reactors made from Fecralloy and impregnated with Rh were studied in partial oxidation (POX) and oxidative steam reforming (OSR) reactions for production of hydrogen or synthesis gas. Temperature profiles obtained along the reactor axis confirmed that the metallic microchannel reactor is able to minimize temperature gradients and pointed to gas phase ignition in front of the reactor as the main reason for reduced syngas production and increased hydrocarbon by-product formation at the highest furnace temperatures. Addition of steam to the reactant mixture (OSR) resulted in increased formation of hydrogen relative to propane converted (S*(H-2)), mainly in accordance with the water-gas shift reaction. Reducing the residence time below 10 ms at 800 degrees C gave increased S*(H-2) and CO selectivity and reduced by-product formation, indicating suppression of the gas phase reactions and possibly also direct formation of H-2 and CO as part of the reaction scheme. The Rh/Al2O3/ Fecralloy microchannel reactor also shows good stability during more than 70 experiments of both POX and OSR with temperature cycling from 300 to 1000 degrees C. (c) 2005 Elsevier B.V. All rights reserved.