Description Reviews Royal Purple motor oil delivers superior protection and improves performance in all four-cycle gasoline and diesel engines. It increases horsepower and torque, saves fuels and reduces heat, as well as wear and emissions. It has unsurpassed oxidation stability that allows for extended oil drains and fewer oil changes, which saves you time and money as well as it reduces the impact on the environment. Royal Purple motor oils are API certified. For those seeking enhanced performance in high performance vehicles not under warranty, we recommend their 5w30 XPR oil Extreme Performance and Racing motor oil. Royal Purple performance advantages come from a blend of synthetic oils plus Royal Purple's proprietary Synerlec technology. This oil is compatible with other mineral and synthetic motor oils. Note: Now in smaller case sizes!