This disclosure provides for compatibilizer compositions that are useful in compounding polypropylenes and ethylene elastomeric copolymers for injection molding applications. The compatibilizer includes a combination of: Component A of polypropylene homopolymers or polypropylene copolymers containing small amounts of ethylene; and Component B of propylene bipolymers with ethylene and/or other a-olefin comonomers, the bipolymer having a relatively high proportion of propylene moieties, for example, 50-75% propylene. Compared to known or conventional compatibilizer formulations, the bipolymer Component B is relatively propylene rich and generally can be used in the injection molding composition in lower concentrations.