Thermal stressing of a Jet A fuel containing triphenylphosphine (TPP) as an additive results in a significant enhancement in thermal oxidative stability. Efforts to elucidate the mechanism(s) responsible for the observed thermal oxidative stability enhancement are reported, Data presented for the reaction of TPP with molecular oxygen show two pathways to be important. In particular, in nonpolar solvents and in the presence of BHT, the data. are consistent with TPP playing an oxygen scavenging role via operation of an electron-transfer-initiated-oxygenation chain mechanism. The significances of these findings to the potential development of a new generation of thermal oxidative stability enhancing additives is discussed.