This paper presents a performance analysis of a 5 kW(el) high temperature polymer electrolyte fuel cell (HT-PEFC) stack. Stack design and sizing is adapted to auxiliary power unit (APU) applications assuming the use of middle distillates. The parameter study comprises the variation of the fuel type (reformate, with pure hydrogen as a reference), the stoichiometry on the anode (1.3-2.7) and cathode (1.25-4.0) sides and the carbon monoxide (CO) concentration (0.9-3.5%) in the reformate. At 0.5 A cm(-2), a coolant inlet temperature of 160 C, stoichiometric factors of 1.3 on the anode and 2 on the cathode side and reformate operation, two interconnected full stacks produced 5 kW of electric power. The focus of the present work is an examination of the robustness of the full stacks through an analysis of the 70 single cell voltages. By comparison to other published operational parameter studies, this paper makes a significant contribution to the application of the methodology not to single cells or short stacks, but to a stack with technical relevance in the high power class. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.