If you buy motor oil, you probably get frustrated sometimes with all the specifications and constant updates to product info... "Do I need a CI-4 a CJ-4 -whats the difference anyways? I know I need 15w40, but why? What is that anyways?"
API stands for American Petroleum Institute, a "national trade group representing all aspects of the oil and gas industries" according to their website .(As an aside their website www.api.org is a great resource for learning about current issues in energy and their impact). Anyway, API certifies that oils meet the requirements set forth by vehicle manufacturers through testing and sampling, etc.
You should ALWAYS DEMAND API Certified product!
The specific symbols and letters on API specs can be a little confusing, so I thought I'd link up a pretty good guide that gives an overview of what info you need to look for and what it means. You can get the guide online By Clicking Here