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The degree of physical deterioration of catalytic converters removed from two groups of motor vehicles with low and high odometer readings have been studied. The changes in the physical and chemical properties between the two catalyst groups were investigated using the XRD, BET and PIXE/PIGE techniques. Thermal damage was the main catalyst deterioration mechanism in both odometer groups. The low odometer group showed near-uniformity in both surface area loss (average 45 %) and degree of CeO2 sintering representing the baseline thermal deterioration from normal vehicle operation. High odometer catalysts displayed more complex deactivation mechanisms involving both chemical contamination and thermal deactivation such as support phase transformation, internal “hot zones” and contaminant-support interactions.