API Engine Oil Classification

This engine oil classification system was created in 1969 by the American Petroleum Institute. People commonly refer to the API classification as the quality classification for engine oils.

In particular, this classification splits engine oils into two types: for petrol engines and for diesel engines. For each of these types there are quality classes that, in essence, describe a specific set of properties and characteristics for the engine oils of each class.

On the label, information about an engine oil's assigned API class is given in a form such as: API SJ, API CF-4, or API SJ/CF-4.

It should be noted that if the label of an engine oil has no information about compliance with any API class, that unquestionably means the engine oil either has no API certification at all, or that the quality class it was assigned is hopelessly outdated.