Temperature-programmed oxidation (TPO) is used to determine the oxidation reactivity of carbonaceous deposits formed on different substrates via the thermal stressing of jet fuel samples. The multiple CO2 peaks in TPO profiles are attributed to differences in the oxidation reactivity of the deposits, which is related to their structural characteristics. This study investigates whether the TPO profiles relate to the characteristics of the deposits formed during thermal stressing, or if they result from chemical alterations of the original deposits during the TPO analysis. This question is important for understanding the substrate effects on carbon deposition from heated fuels, as well as the removal of carbonaceous deposits from the aircraft fuel system components. Findings from this study affirm that the results from TPO experiments can be used to characterize the oxidation reactivity of carbonaceous deposits, relative to their molecular and structural characteristics.