There are 3 primary types of engine oil: conventional, synthetic-blend, or full synthetic. Conventional oil, adequate for most vehicles, offers some protection against deposit build up and viscosity break down. Synthetic-blend (or high-mileage) oil contains a blend of conventional and synthetic oils chemically engineered to extract more impurities than a conventional oil alone. Full synthetic oil is considered by many to be the best type of oil to put in your vehicle. Many synthetic oils feature superior cleansing properties which help keep your engine cleaner.