Royal Purple 0W-40 High Performance Synthetic Motor Oil is an API-Licensed Heavy Duty SAE Motor Oil. Our oil combines premium base oils with proprietary additive technology to create a high-performance motor oil. As a result, it optimizes engine performance and provides superior protection. Royal Purple is one of a few commonly available premium synthetic engine oils that provide the inherent advantages listed above, but Royal Purple synthetic oils go beyond that. Because of the advanced, proprietary Synerlec® additive technology, Royal Purple synthetic oils outperform any other lubricant, including additional premium synthetic oils. Engines run cooler with Royal Purple, and so do the assemblies and other moving parts lubricated with our extensive line of automotive, marine and other various lubricants.