A model equation is developed to predict the cell voltage versus current density response of a liquid feed direct methanol fuel cell (DMFC). The equation is based on a semi-empirical approach in which methanol oxidation and oxygen reduction kinetics are combined with effective mass transport coefficients for the fuel cell electrodes. The model equation is validated against experimental data for a small-scale fuel cell and is applicable over a wide range of methanol concentration and temperatures. (C) 2003 Elsevier B.V. All rights reserved.