Abstract: Pneumatic tire sidewall compositions are disclosed comprising blends of a halobutyl rubber, a high unsaturation rubber and an oil extended terpolymer of ethylene, propylene, and a diene wherein the oil extended terpolymer contains from between 25 to 150 phr of a paraffinic or naphthenic oil. These triblends provide sidewalls of unexpectedly improved flex resistance, even as compared to similar triblend compositions in which similar amounts of oil are included, but in which an oil extended terpolymer is not employed. Furthermore, methods of preparing such compositions are also disclosed comprising preparing an oil extended terpolymer, and then blending that terpolymer with the halobutyl and high unsaturation rubbers.