The aim of this work is to investigate the effect of slight pressure in the range of several tenths of a mm H2O on the electrode reaction characteristics in a molten carbonate fuel cell (MCFC). Two pressurization methods, an inert gas step addition (ISA) and a water head (WH) were employed in this work. ISA increases pressure by adding an inert gas to the electrode, whereas the WH raises pressure by dipping the gas outlet of the electrode into water. ISA also enhances the reactant flow rate at the moment of pressurization, while the WH reduces the flow rate. The two methods revealed that the overpotential depended on the flow rate rather than pressure, indicating that the gas-phase mass transfer controls the electrode reactions. Independence of the overpotential to the slight pressure implies that the pressure does not affect the electrolyte distribution in the cell. This is based on the assumption that the cell is sealed by the impregnation of liquid electrolyte in the matrices between the anode and cathode, and a pressure difference between the electrodes may move the electrolyte to the lower pressure side, affecting the reaction areas and overpotentials. (C) 2003 Elsevier B.V. All rights reserved.