The Bureau of Mines investigated the contribution of selected components and additives of high-temperature aircraft fuels to thermally induced deposits before and after 52 weeks of storage at 130/sup 0/F. Of particular concern was the influence of fuel constituents on thermal stability quality of jet fuels during storage. A microfuel coker test apparatus was used to measure the thermal stability of test fuels and blends. The contribution of selected fuel components, labeled with carbon-14, to deposit-forming mechanisms was determined by radioactive-counting techniques. Twenty-eight blends of the five test fuels with carbon-14-labeled fuel additives or components reached the final stage of storage at 130/sup 0/F and received final analyses for deposit forming tendency. These additives included an amine-type antioxidant, a metal deactivator, and a corrosion inhibitor. Also included in this study group were oleic acid and 1,5-hexadiene. All three additives showed a marked tendency to degrade and react during storage and thermal stress. Oleic acid was found to interact with cadmium present in aircraft fuel systems and produce deleterious effects upon the thermal stability quality of the fuel. Sixteen blends of the five test fuels with nonradioactive components were prepared as part of a special study. Six of these blends contained 1% of selected aromatic compounds, five blends contained an anti-icing additive, and five blends contained an organic sulfur compound. Results showed changes in thermal stability quality of many of the blends containing sulfur compounds. Four additional special studies were performed as preliminary investigations to continued research of jet fuel stability characteristics. Both were designed to improve producers or develop new, improved procedures for thermal stability tests.