Most might already know this, but some may not. The "American Petroleum Institute" is nothing more than the American oil companies, plus companies (domestic and international) that sell to them. It is the US oil company trade group, that's all.
Years ago I worked for a company that manufactured products that were used in the oilfield. The oil companies insisted the product be audited to "API standards" and carry the API logo. The API standard was just a rehash of ISO 900X, but with API-hired auditors. Authorization to use the log was given by passing the audit plus paying a licensing fee for use. I used to be impressed with the API, but now realize it is mostly a money-maker and lobbying arm of the oil companies.
Don't think for one minute, as I once did, that it is a collection of white-coated scientists that are determining which oil is better. The oil companies wouldn't do that to each other. Instead, they grade the products according to performance and make-up.
There is an interesting history of the oil specifying bodies (ILSAC, API, AAMA, JASO, etc.) at
this website that is, not coincidentally, an Amsoil distributor.
Bill
