Emailed ExxonMobil with the question:
"Is Mobil 1 Synthetic oil a Group III oil?"

Response:
"To meet the demanding requirements of today's specifications (and our customers' expectations) Mobil 1 uses high-performance synthetic fluids, including polyalphaolefins (PAO), along with a proprietary system of additives. In fact, each Mobil 1 viscosity grade uses a specific combination of synthetic fluids and selected additives in order to tailor the viscosity grade to its unique requirement."

A simple "yes" or "no" would have been nice