A semi-empirical equation was proposed to simulate the behavior of a direct methanol fuel cell (DMFC). The individual voltage losses in a DMFC due to methanol crossover and the overpotentials of both the cathode and anode can be distinguished. Three sets of experiments were designed and carried out to account for the three voltage losses. The values of each parameter in the model were then calculated and the computation showed that the fitted result and the experimental data were well matched. The relation between each significant phenomena and each parameter is discussed. The model quantitatively identified the major voltage losses to be both the sluggish reaction of methanol oxidation on the anode and the slow oxygen reduction on the cathode. The impact on cell performance by manipulating individual parameters is also discussed. (c) 2006 Elsevier B.V. All rights reserved.