Since the development of the oxidative induction time (OIT) test by former Bell Telephone Laboratories researchers, there have been many studies to broaden its applicability to polymers beyond the original polyolefins. The basic premise in OIT studies is that a detectable oxidation onset is based on the differential reactivity between the polymer matrix and free radical scavenging antioxidants like hindered phenols. This situation does not exist in depolymerizing systems such as polymethylmethacrylates (PMMA), so many researchers concluded that a correlation did not exist for these systems. We will report on the observation of a clear cut, Arrhenius-like oxidative induction time behavior in a toughened PMMA system with high pressure DSC. The relationship between the observed OIT at elevated temperatures and high oxygen pressures with lower temperature oven aging studies will be presented.