An empirical equation [E = E 0-b log i-Rim exp (ni)] was shown to fit the experimental cell potential (E) vs. current density (i) data for proton exchange membrane fuel cells (PEMFCs), at several temperatures , pressures , and oxygen compositions in the. cathode gas mixture. The exponential term compensates for the mass-transport regwns of th~ E vs. z plot; i.e., the increase in slope of the pseudolinear region and the subsequent. rapid fall-off of the cell potential with increasing current density. As has been prevwusly shown, the terms E 0 ~nd b yield the electrode kmetic parameters for oxygen reduction in the PEMFC and R represents the resistance, predommantly ohmic and, to a small extent, the chargetransfer resistance of the electro-oxidation of hydrogen. The exponential term charactenzesthe mass-transport regwn of theE vs. i plot. The parameter n has more pronounced effects than the parameter m m this regwn. A physicochemical interpretation of these parameters is needed.