The effects of single, binary and ternary contaminant mixtures containing propene (C3H6), acetonitrile (CH3CN), and bromomethane (CH3Br) on proton exchange membrane fuel cells have been studied. Changes in polarization curves, electrochemical impedance spectroscopy spectra, electrochemical catalyst surface areas by cyclic voltammetry, and hydrogen crossover through the membrane by chronoamperometry are used to define the extent of recovery and irrecoverable losses after the contamination period and to understand the contaminant interactions. CH3CN in the contaminant mixture mitigates the decrease in oxygen reduction reaction kinetics and the increase in oxygen and water mass transport resistance, while C3H6 speeds up the above situations. The hydrolysis of CH3CN results in the formation of ammonium ions, which exchange with membrane protons, leading to an increase in the membrane resistance. CH3Br increases the decomposition of the Nafion® ionomer. Bromide accumulation on the catalyst surface leads to large catalyst area losses for the mixtures containing CH3Br. Competitive adsorption on Pt active sites exists between CH3CN and CH3Br. However, there is noncompetitive adsorption between C3H6 and CH3Br or CH3CN.