This paper investigates the performance of a high temperature proton exchange membrane (PEM) fuel cell. Both experimental work and numerical simulation are conducted. The high temperature proton exchange membrane is based on polybenzimidazole (PBI) doped with phosphoric acid. A single cell with triple serpentine flow channels was operated at steady state at various levels of temperature, pressure, and air stoichiometry. A three-dimensional model was used to simulate the cell performance, and polarization curves were used to validate the experimental values. The theoretical model accurately predicts the experimental results. A sound knowledge of the impact of various variables at various levels of the cell operation is necessary for unraveling the parametric influence and can prove extremely useful for optimizing the cell operation. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3203309] All rights reserved.