Mass transport is a factor which limits the performance of solid polymer electrolyte fuel cells operating at relatively high current densities, The direct methanol solid polymer electrolyte fuel cell, unlike the hydrogen cell, suffers from mass transport limitations predominantly at the anode. In the liquid feed cell the mass transport limitations arise from diffusion of methanol in the carbon cloth covering the active electrocatalyst layer and from hydrodynamic limitations in the anode flow channel. A model of the methanol mass transport processes is presented which is used to predict the effective methanol concentration at the catalyst surface and thereby the anode polarisation. This model, together with an empirical model of the open circuit voltage and the cathode overpotential model, is used to predict the overall cell voltage, current density response of the fuel cell.