Previous experimental studies have shown that addition of small amounts of oxygen to a hydrocarbon fuel stream can control coking in the anode, while relatively large amounts of oxygen are present in the fuel stream in single-chamber solid oxide fuel cells ͑SOFCs͒. In order to rationally design an anode for such use, it is important to understand the coupled catalytic oxidation/ reforming chemistry and diffusion within the anode under SOFC operating conditions. In this study, the heterogeneous catalytic reactions in the anode of an anode-supported SOFC running on methane fuel with added oxygen are numerically investigated using a model that accounts for catalytic chemistry, porous media transport, and electrochemistry at the anode/electrolyte interface. Using an experimentally validated heterogeneous reaction mechanism for methane partial oxidation and reforming on nickel, we identify three distinct reaction zones at different depths within the anode: a thin outer layer in which oxygen is nearly fully consumed in oxidizing methane and hydrogen, followed by a reforming region, and then a water-gas shift region deep within the anode. Both single-chamber and dual-chamber SOFC anodes are explored. Among the components of a solid oxide fuel cell ͑SOFC͒, the anode presents perhaps the most significant technical barrier to creating an efficient, economic, and environmentally friendly technology that makes better use of readily available fuels.1 Ongoing research has been trying to address these issues by seeking anode materials that possess excellent catalytic, electrochemical, and mechanical properties, and the nickel-zirconia cermet anode is currently the dominant SOFC anode due to its structural stability, small thermal expansion mismatch with popular electrolyte materials, and good catalysis for hydrogen oxidation and steam reforming of hydrocarbon fuels.1 In particular, the anode-supported membraneelectrolyte assembly ͑MEA͒ structure is advantageous for hydrocarbon fuels, because it also serves as a reforming or catalytic partial oxidation catalyst in addition to conducting current.2 However, it is generally impossible to operate nickel-based anodes on higher hydrocarbon-containing fuels, because nickel also catalyzes the formation of carbon filaments ͑i.e., coking͒ from hydrocarbons under reducing conditions, 1 and coking can still occur on Ni catalysts even under thermodynamically noncoking conditions.3 Formation of carbon deposits on Ni particles is responsible for excessively high activation polarization, which leads to the rapid deterioration of cell performance. 4 For example, Zhan et al. reported that the use of iso-octane causes severe coke buildup on the Ni-yttria-stabilized zirconia ͑Ni-YSZ͒ anode and leads to degradation of the anode.3 Various approaches including steam reforming, addition of oxygen to the fuel stream, and incorporation of dopants into the conventional anode material have been tried to mitigate this problem.