Quicksilver outperforms automotive oils in marine applications because of its specialized additive package designed for marine engines.  The NEW mineral 4-Stroke oil is also now approved for use in all outboard engines; previously only our syntetic blend could make this claim. 3 things to know: For use in all 4-Stroke marine engines – New formula 4-Stroke oils are engineering approved for all marine 4-Stroke applications, including: Outboard, Mercruiser, High Performance, Stern Drive/Inboard, and exceeds all marine industry 4-Stroke oil requirements including FC-W and FC-W Catalyst Compatible. Flagship engine and corrosion protection – Industry leading strength and viscocity retention and ultimate corrosion and wear protection . The most recommended marine oil – Over 5 years of engineering and decelopment by the largest marine engine manufacture in the world. 25W40 recommended in all Marine Engines