The thermal degradation of jet fuel is characterized by the formation of particulates and gum deposits. The lack of sensitivity of previous methods of testing thermally stressed jet fuel required acceleration of the test conditions. Recently, two techniques have been integrated into a single instrumented platform to permit simultaneous in-situ real-time measurements of particle-size growth rate and surface mass-deposition rate in these fuels. With this arrangement, the particle growth rate is determined using photon-correlation spectroscopy (PCS), and the surface mass-deposition rate is measured with a quartz-crystal microbalance (QCM). The resolution and sensitivity of these techniques permit the study of particle-size growth rate and mass-deposition rate at temperatures and times representative of those found in aviation fuel systems.