A pyrolysis gas chromatography-mass spectrometry (GC-MS) method was applied for the comparative analysis of 42 samples of rubber collected from passenger car tires. It was found that rubber samples originating from different tires can, in most cases, be effectively differentiated. The rubber samples were first assigned to one of three classes on the basis of the main components present in chromatograms (styrene and limonene). Then peaks obtained from trace constituents of the rubber were taken into account. In most cases, the differences between the analyzed samples were sufficient to distinguish them. In this study, an on-line derivatization technique (using tetramethylammonium hydroxide) was applied. In some cases, this technique made it possible to demonstrate differences that were invisible in normal analysis. The study showed that the pyrolysis GC-MS method was an effective tool to differentiate between samples of tire rubber. The estimated discrimination power without derivatization ranged from 90% (styrene-butadiene rubber based) to 100% (natural/styrene-butadiene rubber samples). Derivatization increased the former discrimination power to 99%.