That would depend on who is forcing me to only have a choice of one oil for the rest of my life. If it's a government thing, I guess I would have to use what they allow the public to use. An employer ? Well, I already have a stock pile of their oil, and am happy to use it, I have no problem with A3/B4 Castrol Edge 5W-30. I don't know any other way I could be forced to use one oil, but if I had to choose, of my own free will...it'd be Penrite HPR 30.