Effects of reactant gas flow rates and starvation on the performance of phosphoric acid fuel cells were studied using single cells. As the reactant gas flow rates of single cell increased, the performance of the cell increased, and then remained constant. The optimum flow rates of hydrogen, oxygen and air under cell operating condition of 150 mA/cm(2) at 190 degrees C were found to be 5 cc/min.cm(2), 5 cc/min.cm(2), and 15 cc/min.cm(2) at 1 atm and room temperature, respectively. The open circuit voltage of the single cell decreased with increasing oxygen flow rate at constant hydrogen flow rate, which is attributed to the increased gas cross-over rate. When the reactant gases were again supplied to the cell after gas starvation, the cell voltage losses were found to be about 5 mV in the case of hydrogen starvation and about 1 mV for oxygen starvation, and the voltage loss was independent of gas starvation time. These results were discussed from the electrochemical viewpoint of the cell.