Localized hydrogen evolution was found in the anode flow field of a liquid-feed direct methanol fuel cell (DMFC) under open-circuit conditions after the oxygen supply was cut off or restarted. More importantly, this phenomenon led to a temporary rise in the performance of the DMFC by as much as 7%. The relationship among oxygen supply interruption, hydrogen evolution, and performance variation has been investigated both theoretically and experimentally. (C) 2005 The Electrochemical Society.