Which API Group classification is associated with Polyalphaolefin (PAO) base stocks in modern synthetic oils?

API Group IV

In the modern context of classifying base stocks, Polyalphaolefins (PAOs), which represent the heritage chemistry pioneered by the early synthetic efforts, are specifically categorized under API Group IV. This classification distinguishes them as true synthesized base stocks, distinct from Group III oils, which are highly refined mineral oils (hydrocracked or severely hydroprocessed) that, despite advanced processing, still originate from crude petroleum. Understanding this grouping helps delineate between the historically pure synthesis route (Group IV) and chemically similar, but distinct, highly processed mineral routes (Group III) currently dominating much of the synthetic market.