The reactivity of crosslinking peroxides decreases in the order 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide, 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(t-butylperoxide)-3-hexyne. First order decomposition rate constants for these peroxides were inferred from oscillating disk rheometer studies in poly(ethylene). The cure reaction in EPR and EPDM is more complex than in poly(ethylene) and the conventional measure of cure time leaves significant unreacted peroxide in the vulcanizate. Quinoline type antioxidants are preferred because they interfere least with the cure reaction.