Asphalt binders are complex mixtures of a wide variety of hydrocarbon materials. Added to this complexity in recent years has been modification with a variety of polymer modifiers. Binders used in this study were commercial materials obtained directly from the suppliers. They include diblock poly (styrene-b-butadiene) rubber (SBR), triblock poly (styrene-b-butadiene-b-styrene) (SBS), and high-cure ground tire rubber. A study of the effect of these modifiers on oxidative aging and on changes in physical properties due to aging shows several effects. Modifiers can reduce oxidative aging rates to some degree, but a bigger effect tends to be to reduce the hardening of binders that occurs in response to oxidative aging. This reduction in hardening rate is expected to have a positive effect on pavement performance over time, relative to the performance of base asphalts. Furthermore, the effectiveness of modifiers varies with the base asphalt.