Thermal stressing experiments on a modified surrogate fuel and synthetic paraffinic kerosene (SPK) have been carried out under both static and dynamic conditions at 140 degrees C. In order to characterize the oxidation products, some key degradation compounds were monitored throughout the stressing experiment. Products resulting from ring closure reactions were also identified in the surrogate fuel and the SPK, with the identification of iso-benzofuranone and alkyldihydrofuranones. Furanones were quantified using gas chromatography mass spectrometry (GC-MS) with high-performance liquid chromatography (HPLC) prefractionation. The formation of these furanones indicates that dynamic stressing promotes a reactivity that has only been reported at either higher temperatures or longer residence times.