High temperature antioxidant additives and methods that improve a liquid fuel composition's thermal oxidative stability are disclosed. A liquid fuel composition may comprise a liquid fuel; and a high temperature antioxidant additive comprising a nitroxide radical having a formula: wherein R1, R2, R3, and R4 are individually selected from an alkyl group or a hetero atom substituted alkyl group, and wherein R5 and R6 are any atom or group except hydrogen which can bond covalently to carbon.