Polyethylene compounds for industrial applications are typically crosslinked via a radical pathway by means of a radical initiator, such as dicumyl peroxide. The compositions also contain additives designed to improve heat-aging performance. However, due to interactions with the peroxide, some of these additives can negatively affect peroxide stability in the polymer compound product. Using dodecane as the model for polyethylene, the current work examines the kinetics and product distribution associated with the thermal decomposition of dicumyl peroxide in the presence of several costabilizers in air and under a nitrogen atmosphere. Mechanistic explanations based on the experimental observations will be presented.