The methanol oxidation has been studied on high index (755), (211) and (311) and low index (111) platinum surfaces in perchloric and sulfuric acid. The most active of the stepped surfaces is (755) in both acids. (755), (211) and(lll) surfaces are more active in perchloric than in sulfuric acid. The Pt(311) plane shows the same activity in both acids. Methanol is preferentially adsorbed competing with sulfuric acid anions. The oxidation of methanol proceeds without any important effect caused by specific adsorption of sulfuric acid anions at lower anodic potentials. The presence of a reactive (OH)(ads) species on the surface seems to be the major cause for the larger activities of the electrodes at higher anodic potentials. Two different reaction mechanisms are proposed for the Pt(755) plane. The poisoning species formation dominates at the potentials lower than E = 0.25 V (see). The oxidative removal of poisoning species followed by the bulk methanol oxidation at the surface partially covered by (OH)(ads) species take place at the more positive potentials. The increase of (OH)(ads) coverage, and the formation of inactive oxygenated species cause the inhibition of the methanol oxidation at potentials more positive than the peak potentials.