Hydrogen quality is critical for increasing the reliability, stability, and durability of polymer electrolyte (PEM) fuel cells. In this work, several hydrogen impurities have been studied to understand their effects on PEM fuel cell performance at various operating concentrations. Our studies have shown that the following impurities suggested by industry stakeholders do not result in substantial fuel cell degradation when they are the sole impurity in hydrogen: 5 ppm formaldehyde, 2 ppm formic acid, 19 ppm chloromethane, 30 ppm acetaldehyde, 5% ethylene, 20 ppm toluene, and 10 ppm benzene. In addition, a specific mixture of impurities called the "specification concentration level cocktail" consisting of 0.2 ppm carbon monoxide, 4 ppb hydrogen sulphide, 0.2 ppm formic acid, 2 ppm benzene, and 0.1 ppm ammonia in hydrogen, also does not show significant effects on cell performance. In comparison, when a cocktail having five times the specification concentration is introduced into the cell, significant performance loss is evident. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.