Our objective is the understanding of the mechanisms of formation of polycyclic aromatic hydrocarbons (PAH) inside the pre-combustor fuel systems of hypersonic aircraft, where the pressure and temperature exceed the critical values of most hydrocarbon fuels. Since PAH are precursors to carbonaceous solids, they are key to the elucidation of the reactions leading to the formation of these solids, which obstruct fuel lines and lead to undesirable effects for the aircraft. We have applied high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance and mass spectrometric detection to analyze the products of a synthetic jet fuel pyrolyzed at 710°C and 42 atm in a scramjet test rig. Benzo[ghi]phenanthro[9,10,1-cde]perylene, for example, has been identified using the Annellation Theory developed by Clar and the information obtained from the ultraviolet-visible and mass spectral analyses. This is the first time that this PAH has been identified as a product of the reaction of any fuel.