Waste polypropylene (PP) has been pyrolysed to obtain mainly a liquid tar product of high yield (83.5%) with the balance as gas (15.5%) and a little residue (1.0%). The elemental composition of the PP tar was: C: 87.1%, H: 12.6% and O+others: 0.4% (by difference). The tar samples have been characterised by gas chromatography/mass spectrometry, heated-probe mass spectrometry and laser desorption mass spectrometry (LD-MS), to give molecular mass distributions for comparison with molecular mass ranges indicated by size-exclusion chromatography (SEC). About 50% of the tar was soluble in 1-methyl-2-pyrrolidinone, the solvent used for SEC. It appeared to consist mostly of low molecular mass materials with elution time at 20–27 min. Mass ranges from SEC and LD-MS agreed approximately in showing the upper mass limit of the tar to be about 1200 u, consisting of aromatics, alkenes, dialkenes and only minor quantities of alkanes.