The deposits formed after short durations of pyrolytic degradation consist of carbonaceous solids growing oil metal sulfide particles. Carbonaceous solids contain amorphous films and uniformly sized spheroids. Close association of the carbonaceous film with the sulfide particles suggests that it was produced by a heterogeneous process similar to chemical vapor deposition (CVD), while the morphology of the spheroidal deposits suggests that they were formed by homogeneous nucleation and growth in the fluid phase. Thermal stressing on an alumina-coated SS3 16 surface and reducing the sulfur content of the jet fuel from 0.10 to 0.01 wt % inhibited metal sulfide formation on the surface. This consequently inhibited the growth of film deposits but not the nature or amount of fluid-phase deposits. These results have shown that the sulfur content of jet fuel and the substrate composition control the heterogeneous carbon deposition. These parameters do not affect the nucleation and growth of the fluid-phase deposits.