From petroleum based to full synthetic, Sierra has the correct engine crankcase oil to match the needs of your gasoline or diesel inboard or sterndrive engine. Sierra offers a full line of direct replacement weight oils that are specifically blended to protect your engine in the harsh marine environment and the extreme load conditions that your engine is subjected to every time you push down on the throttle. Unlike automotive engine oils, Sierra oils are specifically designed to prevent moisture and corrosion from harming your engines internal components. Best of all when you choose Sierra engine oil, you can feel confident that our marine specific oils are backed by the Sierra’s Industry Leading Warranty. Remember when it comes to oil you do have a choice, so choose Sierra!