You have to be carefull because Castrol does make two different types of oil with the words synthetic on the bottle...
1. Syntec Blend
2. Syntec
The correct bottle to chose would be the one that says "Syntec; Full Synthetic Motor Oil"
Sorry if I'm being sarcastic..... Castrol vs. Mobil 1 is like Ford vs. Chevy... they are both the same, just user preference. I think the two main reasons why I prefer Castrol are
1. BMW uses it for their factory fill
2. The Exxon Valdez spilled 11 million gallons of oil into the Prince William Sound.