The fuel cell performance effects of many contaminants originating from multiple sources such as air, fuel, and system materials release need to be determined to reduce risks associated with market introduction. A significant amount of time and resources are required to test the performance effects of all possible contaminants because contaminant impacts develop slowly at concentrations reflecting practical operation. Thus, a two tiered down selection process was proposed to identify specific contaminants for more detailed studies. The methodology used to generate the second tier down selection is presented and discussed in relation to a specific contaminant, sulfur dioxide. Two quantitative criteria were derived based on parameters defined using the cell performance response to a temporary contaminant injection. These quantitative criteria were applied to sulfur dioxide data to investigate the effects of different operating conditions and determine the most relevant selection criterion. Results showed that the method which considered the ratio of the energy lost during contaminant exposure to the energy recovered subsequent to the contaminant exposure is preferable in this case because values are less dependent on operating conditions. Furthermore, the energy lost to energy recovered ratio is also preferable because high values not only identify the contaminants with the most significant performance loss and least performance recovery but also identifies contaminants with a performance recovery that exceeds the performance loss. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.