The effect of stoichiometric ratio lambda on performance of a polymer electrolyte fuel cell is rationalized. lambda --> infinity corresponds to uniform oxygen concentration along the channel; the limiting current density then is determined by transport of oxygen across the cell. Finite lambda corresponds to decreasing oxygen concentration along the channel. In that case j-axis of a voltage-current plot is "compressed" by a factor f(lambda) = -lambda ln(1-1/lambda) and apparent value of limiting current density appears to be f(lambda) times lower. The function f(lambda) --> infinity as lambda --> 1; physically, in this limit all available oxygen is consumed close to the channel inlet and apparent limiting current tends to zero. Recently derived expression for the voltage-current curve of the cell is extended to take into account the effect of lambda. Fitting of experimental voltage-current curves with the new relation gives an estimate of basic parameters of the cell. (C) 2003 Elsevier Ltd. All rights reserved.