Depends on who's definition of synthetic you use:Considering some other comments here, what oils are "full synthetic" and have there ever been any that are 100% synthetic?
Castrol or Mobil.
Castrol calls their Group III basestock oils as synthetic which Mobil disagrees as they feel Group IV PAO is synthetic.
As there been any others that are fully 100% synthetic? Amsoil likes to claim this, before they diluted the lineup with the OE series oils. There's redline oils, until they started with their Professional Series oil. And of course, Mobil, until after they lose their case with Castrol, and started to dilute their PAO basestocks with Group III base stocks, iirc, starting around the "Tri-Synthetic" version of Mobil 1