I read an interesting paper published by Chevron that does a good job of explaining the differences between the groups as well as the ruling regarding the marketing of "synthetic" oils.

Particularly interesting was, "...in North America due to the recent ruling by the National Advertising Department of the Better Business Bureau that Group III base oils can be considered "synthetic" and because modern Group III base oils, made using hydroisomerization technology, have most of the attractive performance features of early synthetics."

So, because they can make dino oil act like an early Group IV oil (PAO) using a modern hydrocracking process, they can market it as "synthetic".

I couldn't find anything reliable regarding wether Mobil 1 changed their formula to a Group III (I use Mobil 1 5W-30 Truck & SUV). I could only find forum after forum claiming they had. Do you have a link Homeslice?