Castrol syntec 的機油 建議您可看這篇文章中的 "Group II and Group III oils"這一段 http://motorcycleinfo.calsci.com/Oils1.html
以及bob is the oil guy的解說
1992 CASTROL introduces Syntec SAE 5W-50 motor oil based on PAO 1992 CASTROL reformulates Syntec motor oils with API Group III (petroleum) base stock from Shell
In January 1998 CASTROL started to use much cheaper hydroprocessed petroleum base oils from SHELL. Mobil lost the opportunity to sell PAO to CASTROL. Mobil Oil complained to National Advertising Division of the Council of Better Business Bureaus, which in April 1999 finally ruled in CASTROL favor, specifically allowing Syntec Motor Oil made from SHELL XHVI slack wax stream to be sold and promoted as "synthetic". To celebrate the victory, CASTROL Company spokesperson said: "CASTROL is proud to be a major worldwide provider of synthetic formulated lubricants, and looks forward to continued participation in this exciting market.