How To Identify Quality Motor Oil


When choosing oil for your vehicle, you should always look or ask for API-licensed oil. API has made it easy to find these oils: licensed oils display one or both of the API motor oil quality marks—the API Service Symbol “Donut” and the Certification Mark “Starburst.” These marks are part of API’s Engine Oil Licensing and Certification System (EOLCS), a voluntary licensing and certification program that authorizes engine oil marketers meeting API requirements to display the API quality marks.


The API “Donut” identifies oils that meet current API engine oil standards. It includes the SAE viscosity grade of the oil, API standards met by the oil, and other important performance parameters.

  • The top of the “Donut” displays the motor oil’s API performance standard. The letter “S” followed by another letter (API SN) refers to oil suitable for gasoline engines, and the letter “C” followed by another letter and number (API CJ-4) refers to oil suitable for diesel engines.
  • The center of the “Donut” shows the motor oil’s SAE viscosity grade. Viscosity is the measure of an oil’s ability to flow at certain temperatures.
  • The bottom of the “Donut” tells whether the motor oil has resource-conserving properties when compared with a reference oil in an engine test. Motor oils labeled as “Resource Conserving” have passed this test.


The API “Starburst” signifies oils which meet the latest International Lubricant Specification Advisory Committee (ILSAC) standard. The ILSAC standards are developed by vehicle and engine manufacturers, oil and additive companies and industry trade associations such as API, ACC, ASTM and SAE. These oils provide engine protection while also delivering improved fuel economy and emission system protection.