What api service letters -oil?

The American Petroleum Institute (API) assigns service letters to classify motor oils based on their performance and suitability for use in engines. These service letters, such as "API SN" or "API SP," indicate the oil's quality level and its compatibility with various engine types. The letters are often accompanied by a "resource conservation" designation (e.g., "API SN Resource Conserving") to denote oils that promote fuel efficiency. Overall, these designations help consumers choose the right oil for their vehicles.