Oil guru's...I had emailed shell rotella's tech dept a while back with a question wondering what base group the T6 was? I had heard rumors of a group III "plus" or something like that supposedly "better" then a typical group III...my response from them was what I had expected...on how they cannot disclose this info due to being 'proprietary info" and how they are a "full synthetic" ....with that being I am surprised that they allow the company "auto-rx" to post that they are INDEED a group III oil. If you look on the "auto-rx" website under what oils to use during the cleaning phase...they list all group III oil's including shell. For some reason they state that these group III oils are better then higher group oils for use with this product. Not trying to start a "group war" now....but am just trying to clear the air for some others who were wondering the same. I also am not bashing this product, as I currently am using it myself...a UOA in the future will tell me how it's holding up. Perhaps shell tech dept should just answer people how they want when asked... do they really believe if you know what base oil they use that you are gonna some how copy them? After all we do see VOA's/UOA's from them! -Peace