There are no PAO (polyalphaolefin) synthetic molecules in Castrol Syntec, yet because of legal finagling with the definition of synthesized motor oils they can legally be called synthetic. Basically, they changed the definition of a synthetic to fit the process of highly refining a petroleum base oil, called hydrocracking and fought with Mobil and the National Advertising Council to loosen the definition of a synthetic.
Castrol Syntec is fine oil…it just is not a PAO synthetic oil.