I've always wondered about this...how does one find this info out? The product spec sheets don't list base oil groups and percentages, of course. And the MSDS's only mention broad oil types, and not specific base oil groups, from my recollection. Most info on oil groups in this board seem to go along the lines of, "I've heard that Brand X oil is about 50% Group II," etc., not exactly definitive sources of info when compared to manufacturers' spec sheets and the like.