Reaction of the organic sulfur compounds in Jet A with Fe- and Ni-based alloy substrates under pyrolytic conditions formed significant amounts of metal sulfides. Pyrrhotite (Fe(1-x)S) and heazlewoodite (Ni3S2) were formed on SS316 and Inconel 600 Surfaces, respectively, in the short duration experiments. After extended periods of thermal stressing, an additional crystal phase, pentlandite (Fe,Ni)(9)S-8, was also observed on both surfaces. The lack of FeS2 (pyrite) formation over extended periods of stressing indicates that the amount of sulfur reacting with the substrates decreased with the increasing thermal stressing time. A focused ion beam (FIB)/SEM analysis showed that the metal sulfide formation can extend up to 2 mu m depth from the surface in 2 h of thermal stressing. The formation of metal sulfides on alloy surfaces degrades the alloy surfaces and affects solid carbon deposition from jet fuel.