Tooslick posted this on another forum and it really struck me that it's not really discussed. We all know that Group III basestocks are considered synthetics. But the question is: "Is a group III closer to a group III or a Group IV in respect to performance and cost"? Let try to take something like Chevron that has a group II as their primary motoroil basestock and their synthetic version is still only a Group III. As compared to something like Mobil 1 or Amsoil that is PAO/Ester based.