The Bureau of Mines developed a radiotracer method for detecting the contribution of selected components and additives to thermally induced deposits of turbine aircraft fuels. Of particular concern was the influence of aromatic hydrocarbon fuel constituents on thermal-stability quality of jet fuels during storage. A microfuel coker test apparatus was used to thermally stress the test fuels and blends, and the resultant contribution to deposits of selected fuel components, labeled with carbon-14, was determined by radioactive- counting techniques. Ninety-one blends of five test fuels with carbon-14-labeled fuel additives or components were prepared, tested, stored for 52 weeks at 130 deg f, and reanalyzed for deposit- forming tendency. These additives included two antioxidants, a metal deactivator, and a corrosion inhibitor. Of the fuel systems studied, the greatest reaction was observed in blends containing methyl- and ethyl-substituted indenes. Three of the additives showed a marked tendency to degrade and react during storage and thermal stress. A cresol antioxidant, however, barely contributed to deposit formation. Oleic acid interacted with cadmium present in aircraft fuel systems and produced deleterious effects upon the thermal-stability quality of the fuel.