Hydrogen production through autothermal reforming (ATR) of hydrocarbons, such as methane, is an attractive option for mobile applications of hydrogen fuel cells. In the present study, a numerical investigation of catalytic autothermal reforming of methane in a surface microreactor is presented. The microreactor is intended for use in a micro-fuel processor device for a low-power PEM fuel cell in a mobile application. A three-dimensional ATR reactor model is developed to simulate the flow and surface reactions in a microchannel of square cross-section. A four-reaction mechanism is implemented to simulate the surface reactions on a Ni/Al2O3 catalyst, and a global mechanism is used to model gas-phase methane oxidation. The governing equations in the model include conservations of mass, momentum. energy and chemical species. The simulation results reveal the dependency of hydrogen yield on space velocity (SV), air/fuel molar ratio (A/F), water/fuel molar ratio (W/F), and the feed gas temperature. The optimum conditions for the highest hydrogen yield were obtained in our simulations as: space velocity of 50,000 h(-1), A/F of 1.0, W/F of 3.0 and feed gas temperature of 600 degrees C. The carbon monoxide production at these conditions is small enough to make the generated synthesis gas suitable for fuel cell applications after further treatment downstream of the ATR microreactor. (C) 2010 Elsevier B.V. All rights reserved.