The objective was to investigate PAH emissions in diesel particulates using two diesel fuels with different PAH content. Class A2 diesel from two different refinery sources were analysed for PAH and there were significant difference in the concentration of the 3 and 4 ring PAH of importance in particulate PAH emissions. One fuel had at least 20 times the benzo[a]pyrene (BaP) of the other. A mass balance between the fuel PAH input to the engine and the particulate PAH emissions was carried out. A similar mass balance was also carried out between the equivalent boiling point n-alkane fuel and particulate SOF, which determined how that distillation fraction of the fuel behaved in the engine. One of the fuels had a higher survivability of high MW n-alkanes and this was also reflected in the PAH emissions. The fuel with high BaP had BaP emissions entirely consistent with an unburned fuel source. It was concluded that the dominant source of PAH emissions in the particulate SOF was unburned fuel PAH. Fresh PAH free lubricating oil was used throughout in an attempt to eliminate additional sources of PAH.