The thermal stability of a high-quality hydrotreated Jet-A fuel, an average-quality straight-run Jet-A fuel, and several blends of each fuel has been studied during flow through a single-pass tubular heat exchanger at 185 degrees C. The goal was to obtain fundamental information concerning the thermal stability of fuel blends using dynamic isothermal methods. Autoxidation was tracked as a function of stress duration by measurements of dissolved oxygen and hydroperoxides; insoluble formation was determined by measurements of the average surface deposition rate and the total quantity of bulk insolubles collected on in-line filters. On the basis of several thermooxidative stability criteria, some of the blends were found to be less stable than either neat fuel. Furthermore, benefits of blending were not realized until the lesser-quality fuel had been diluted more than 8-fold. The implications of blending high- and lesser-quality fuels are discussed in the context of autoxidation and insoluble formation.