A method of simultaneous measurement of multiple electrochemical parameters was employed to examine the lifetime operation of direct methanol fuel cells (DMFCs), which includes not only time duration, operational voltage and current, but also the fuel crossover, energy density, cumulative capacity, and cumulative energy. The lifetime performance of two types of DMFCs under different operating conditions was quantitatively compared based on their maximum capability to generate electric energy. A phenomenon of delamination between the anode electrode and electrolyte membrane was observed during lifetime operation. The long-term effects of heat, methanol solution, and CO2 gas may gradually reduce the binding force between the anode electrode and the electrolyte membrane until its physical separation, which results in gradual increase of the resistance of the interface and causes discharge performance degradation. Such performance degradation from the anode side is apparently different from that of ruthenium crossover, which was previously reported, that inhibits the catalytic reduction of oxygen by the presence of ruthenium on the cathode catalyst. (c) 2006 The Electrochemical Society.