The microscopic reaction mechanism for methanol oxidation on Au(1 1 1) surface has been thoroughly investigated by means of density functional theory (DFT) computations. The adsorption geometries and energies were obtained for all the adsorbates, including the reactants, the products, and various possible intermediates on the metal. According to different oxygen conditions, we propose two possible reaction pathways for methanol oxidation on Au(1 1 1): (1) HCHO esterification: the intermediate formaldehyde and methoxy couple to yield methyl formate at low oxygen coverage or without the presence of oxygen atoms; (2) HCHO oxidation: the formaldehyde is oxidized to form formate at high oxygen coverage, which further dissociates to give CO2. Our study emphasizes the critical role of oxygen coverage during the methanol oxidation reaction, and can perfectly explain the difference in product distributions observed in previous experiments. (C) 2012 Elsevier B.V. All rights reserved.