A simplified mathematical model for an ion-exchange membrane attached to a gas-fed porous electrode is developed to simulate the oxygen electrode of a solid-polymer-electrolyte fuel cell. In particular, the present model is derived from an earlier rigorous one of Bernardi and Verbrugge (1991) by neglecting the Peclet number for the transport of dissolved oxygen within the catalyst. The advantage of this simpler model is that it can be solved analytically, eliminating the need for numerical simulation. Longitudinal profiles for the dissolved oxygen concentration and catalyst current density calculated from the present model are in good agreement with results from the earlier rigorous model.