5. API classifications

The first American Petroleum Institute (API) motor oil classification system dates back to 1947. It classified them according to their formulations into: Regular (pure mineral), Premium (rust- and oxidation-inhibited mineral) and Heavy Duty (detergent mineral) oils.

The second API classification system, in force from 1952 to 1970, was based on the severity of engine service. Gasoline engine oils were classified as ML (Motor Light) for light duty, MM (Motor Moderate) for moderate duty and MS (Motor Severe) for severe duty. Diesel engine oils were classified as : DG (Diesel General), DM (Diesel Moderate) and DS (Diesel Severe).

The third system of "engine oil and engine service performance classifications", in force since 1970, is published by the Society...