Exhaust polycyclic aromatic hydrocarbons (PAHs) were experimentally investigated on a single cylinder diesel research engine which was based on a commercial light duty, high speed, automotive engine. Experiments were carried out on the engine at a constant speed of 1200rpm and 7bar IMEP. The study was supported by separate experiments conducted in a tube reactor, aimed at understanding PAH formation processes under conditions which were less complex and less difficult to access as those in the diesel engine. Particulate matter and gas phase PAHs were generated in the tube reactor at temperatures ranging from 1050 – 1350 °C under oxygen-free pyrolysis; to a degree, the conditions in the reactor resembled those in the core of a diesel engine spray, where a significant proportion of the particulates are generated during diffusion-controlled combustion. The diesel engine and the tube reactor were supplied with fossil diesel fuel, as well as single component and binary model fuels prepared by blending various proportions of toluene into heptane. PAHs were extracted from both the engine exhaust and the reactor effluent gas. The PAHs extracted were those adhering on the surfaces of the particulates as well as those PAHs found in the gaseous state in the exhaust/effluent gas. The extracted PAHs were analysed and quantified using gas chromatography coupled to mass spectrometry (GCMS). The Investigation covered the 16 US EPA priority PAHs, with particular emphasis given to the B2 subgroup of PAHs which are considered by the EPA as possible human carcinogens.