Mobil did call Castrol out and sued them. Unfortunately Mobil lost the suit and within 2 years changed most of their syn oils to Group III petroleum oils instead of Group IV and V syn oils. This was done so they could compete with Castrol & Vavoline.

Shell Rotella T oil is a good oil, but only a good Petroleum oil. There are large differences between Petroleum oils (Group I, II & III) and Syn oils (Group IV & V) that no amount of refining can over come.

Tom

Those who would give up essential liberty to purchase a little temporary safety deserve neither liberty nor safety. Benjamin Franklin, US author, diplomat, inventor, physicist, politician, & printer (1706 - 1790)