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Ray O, I was surprised to learn this, but Amsoil does apparently carry 2 lines of API-*certified* oil: one gasoline line and one diesel line, according to the Wikipedia entry on AMSOIL.
The gasoline engine line of API-certified products begins with XL. The 5w-30 viscosity would be XLF.
Some of the Wiki entry:
"Another common misconception is that motor oils must be API certified in order to meet warranty requirements. The fact is, lubricants are not required to be certified by the API, only meet or exceed API specifications. An API license indicates that a specific motor oil formulation has passed the minimum performance standards as defined by a series of laboratory bench tests that include physical, chemical and engine tests.
"API licensing was originally developed for mineral-based oils. Petroleum motor oil companies can take advantage of the convenience and flexibility associated with base stock interchange, which allows them to buy petroleum base stocks from any number of suppliers without being required to re-test and re-certify their products. This ensures adequate supply and competitive pricing. Most synthetic base stocks, on the other hand, are supplier specific and base stock interchange is not allowed. If, for instance, if AMSOIL wanted to blend an API-approved motor oil using the same type of base stock from a different supplier, the oil would have to be re-tested and re-certified."