A simple mathematical model, based on the basic chemical reactions and mass transfer, was developed to predict some important characteristics of molten carbonate fuel cells (MCFC) with LiNaCO3 and LiKCO3 electrolytes for steady state operating conditions. The parallel and cross gas flow patterns were analyzed. Model simulates polarization characteristics, the effect of temperature, pressure and electrolyte type on the cell performance, various losses in the cell and gas flow rate changes through cell. The effect of fuel utilization on the cell potential and efficiency was also analyzed. Model predicts a better performance for the MCFC with LiNaCO3 electrolyte and the cross flow pattern, in general. Results show a strong influence of the operating temperature on the cell potential at temperatures below 625 degrees C, where cell potential increases rapidly with increasing temperature. Above this temperature, however, the cell potential has almost a steady asymptotic profile. The model predicts cell efficiency steadily improving with increase in fuel utilization. The cell potential decreases almost linearly with increase in the fuel utilization percentage for both electrolytes. Models results show a stronger dependency of the cell potential on the operating pressure than that described by the Nerst equation which is in line with fact that the real variations in the cell potential can be higher due to decreased various losses. (c) 2007 Elsevier B.V. All rights reserved.