This paper presents a mathematical model of the corrosion of carbon catalyst supports in polymer electrolyte membrane (PEM) fuel cells. The model describes how a maldistribution of hydrogen across the fuel electrode can induce both oxygen evolution and carbon corrosion on the positive electrode of the fuel cell in the fuel-starved region. Implications of this reverse-current mechanism are explored by simulating a cell with a nonuniform distribution of hydrogen along the fuel channel in both steady-state and transient operation. (c) 2006 The Electrochemical Society.