The effects of storage in the presence of copper using laboratory test conditions vs field conditions on fuel thermal stability were compared using five JP-5 fuels. Laboratory test conditions refer to accelerated storage at 90 degrees C/50 psig of air/24 h in the presence of soluble copper from copper(II) ethyl acetoacetate (CuEA). In contrast, field conditions refer to long-term storage at room temperature (similar to 20 degrees C) in the presence of dissolved copper from 90/10 copper-nickel (Cu-Ni) alloy for a period of approximately 6 months. Thermal stabilities were determined using the gravimetric JFTOT, which gives a quantitative measure of the total deposits formed. A copper concentration/storage effect was observed, which necessitated evaluations at similar copper concentrations. However, the source of copper appears not to be important. Instead, the main operative factor affecting the thermal stability of stored fuels appears to be the combination of long-term ambient storage and the presence of copper. Good agreement was obtained between the thermal stabilities of fuels that were stored using the specified laboratory and field conditions. These results are significant because (1) they validate the use of the specified laboratory test conditions as being realistic; (2) they support our premise that precursors that lead to thermal deposits are formed on storage in the presence of copper; and (3) they offer a rigorous method for predicting the potential thermal stabilities of jet fuels.