Jet fuel tends to form solid deposits when exposed to elevated temperatures and pressures in an oxidative environment during jet engine operation. These solid deposits can cause operational and maintenance problems in fuel system components and, in extreme cases, engine failure. In this study, the degradation of a commercial aviation fuel, Jet A, a predominantly aliphatic fuel, deposited carbonaceous solids that consist of condensed polyaromatic hydrocarbons at relatively low temperatures under oxidative conditions in a flow reactor. The deposit particles exhibit a spherical morphology indicating their formation in the fluid phase. The particles consist of condensed polyaromatic hydrocarbons with varying degrees of structural order. Microscopy and electron diffraction studies showed that the internal structure and the interlayer spacing of these deposits are comparable to certain types of diesel soot. The formation of solids under oxidative conditions led to the incorporation of oxygen functional groups on particle surfaces.