The successful development of a methanol/air fuel cell requires optimum performance of the air/ oxygen cathode at about 0.8 V vs RHE. Ideally the operating potential should be even more positive but oxygen gas reduction on platinum (the best electrocatalyst for this reaction to date at low pH) is generally severely inhibited above 0.8 V. It was demonstrated that in the region of interest the performance of platinum dispersed on carbon prepared by a thermal reduction technique was much superior to that of a similar material in which the platinum was dispersed on carbon by a wet chemical procedure. With the latter material the surface is apparently too reactive : surface platinum atoms of quite low lattice coordination number spontaneously oxidize to yield incipient hydrous oxide species that inhibit the oxygen gas reduction process to potentials below about 0.6 V vs RHE, at which point this oxide is unstable with regard to reduction. The superior performance of the slightly sintered material may be attributed to the lower tendency of the slightly less reactive surface to spontaneously form the inhibiting oxide.