German Castrol 0w-30. It's a unique product of Castrol. The majority of Castrol 0w-30 you'll find in stores is energy conserving group 3 oil, but the GC is a thick 0w-30 that meets many European specs and speculation is that it's PAO/ester/good stuff.
The majority of Castrol 0w-30 you'll find in stores is GC. Check out your local AutoZone.
This is how GC is being distributed in the U.S.
For more info check out the GC forum.
BTW GC is a group IV/V blend. It's a fact, not a speculation.
Yes, the new formulation i.e. the "gold" stuff is full group IV synthetic, not group III. In addition, and please correct me if I'm wrong, isn't ALL 0w-30 produced by Castrol GC? All the other Syntec viscosities are produced in the U.S. and are group III.