The major functions of bipolar plates in fuel cell systems are to transport effectively the reactants and the Products to and from the electrodes, and to collect efficiently the current that is generated in the cell. A Suitable approach to enhance the performance of the bipolar plate with respect to mass transport is to optimize the channel dimension and shape. In this study, the impact of the cathode channel depth on the performance of direct methanol fuel cells is investigated. When the channel depth of the bipolar plate is decreased from 1.0 to 0.3 mm, the cell performance increases and also remains stable during continuous operation of the cell. The decreased channel depth leads to an increase in the linear velocity of the reactants and products at a given volumetric flow rate that, in turn, facilitates their miss transport. Furthermore, in smaller channels (shallower channels), the pressure drop is increased and this call lead to an increase ill partial pressure of the oxygen, which has a positive impact on cell performance. The effect of cathode channel depth oil the transport behaviour of reactants and products is Studied by means of employing the transparent plates, which are designed to monitor visually the flow of reactants and products in the cathode channels. Additionally, the pressure drop and linear velocity in the cell is calculated by using a computational fluid dynamics (CFD) technique. (C) 2008 Elsevier B.V. All rights reserved.