An investigation of the thermo-oxidative stabilization of ethylene–propylene–diene monomer (EPDM), polybutadiene, and emulsion styrene–butadiene rubbers (SBR) with a large number of variously substituted phenolic antioxidants disclosed a limited number of specific antioxidants to be remarkably effective as processing and storage stabilizers for the unsaturated elastomers. The most effective antioxidants of this investigation promise to provide better stabilization of unvulcanized rubbers than currently achievable with present stabilizers. Stabilizer performance in EPDM was assessed by both carbonyl absorbance and gel content measurement after oven aging at 100° and 150°C. Gel measurement after oven aging was found most useful for the other two elastomers. In all instances, good correlation was found between onset of gel formation and onset of color development. The specificity of stabilizer performance is interpreted in terms of functionality, compatibility, stability, and volatility.