The American Petroleum Institute (API) represents all aspects of America’s oil and natural gas industry, having more than 625 corporate members from all segments of the industry, from the largest major oil companies to the smallest of independents. These include producers, refiners, suppliers, marketers, pipeline operators and marine transporters, as well as service and supply companies that support all segments of the industry.

For consumers, API provides the API’s Engine Oil Licensing and Certification System (EOLCS). It is a voluntary licensing and certification program that authorizes engine oil marketers who meet specified requirements to use the API Engine Oil Quality Marks. These emblems go directly on each container of oil that retains the certification for and is there to help consumers identify quality engine oils for their gasoline- and diesel-powered vehicles.

The API engine oil specifications are used throughout the world and also used by many OEMs as the baseline performance upon which their own performance requirements are built.