This paper presents a mathematical modeling of catalytic autothermal reforming (ATR) of methane (CH4) for hydrogen (H-2) production. ATR is essentially an oxidative steam reforming, which combines the exothermic partial oxidation (PO) with the endothermic steam reforming (SR) under thermally neutral conditions. A two-dimensional reformer model is developed to simulate the conversion behavior of the reformer. The model covers all aspects of major chemical kinetics and heat and mass transfer phenomena in the reformer. Results show that the performance of the reformer is dependent on the molar air-to-fuel ratio (A/F), molar water-to-fuel ratio (A/F), and the space velocity of the feedstock mixture. The optimal conditions for high CH4 conversion and high H-2 yield are at A/F of 3.5, W/F of 1, and space velocity of 20000/h. Under this condition, CH4 conversion of 98% and H-2 yield of 42% on dry basis can be achieved and 1 mol of CH4 can produce 1.9 mol of H-2 at an equilibrium reformer temperature of around 1000 K. (C) 2004 Elsevier B.V. All rights reserved.