This work presents, for the first time, the evaluation on the oxidation stability of synthetic oils for an aircraft engine using the rapid small-scale oxidation test (RSSOT) method. Polyol ester lubricants with and without additives were oxidized at 423 K and 7 bar. The pressure drop plots show that during the first period of thermal degradation, the consumption of oxygen is similar for both samples. This part corresponds to the initiation steps of the mechanism of oxidation. Then, the curve of the oil without additives reveals an increase in the depletion of oxygen, corresponding to the kinetic propagation step. Because of the presence of antioxidants, this phase is not observed for oil-containing additives. The RSSOT method also allows us to quantify the time needed for the ester base to produce enough free radicals in order to propagate the mechanism of oxidation. A methodic comparison with other samples containing the raw oil and one additive is also proposed.