API is the American Petroleum Institute, which represents America’s oil and natural gas Industry including performance certification for motor oils. Gasoline engine oil categories fall under the ‘S’ (‘Service’) categories e.g. SN, SM, SL. Diesel engine oil categories fall under the ‘C’ (‘Commercial’) categories e.g. CJ-4, CI-4, CG-4. The EC or “Energy conserving” rating applies to gasoline-engine cars and light commercial vehicles. Use of EC oil may result in an overall saving on fuel in the vehicle fleet as a whole.