I foresee two possibilities. One, mixing different brands of oils of the same weight causes your engine to be lubricated and you are happy. Or two, the encounter could create a oil paradox, the results of which could cause a chain reaction that would unravel the very fabric of the space time continuum, and destroy the entire universe! Granted, that's a worse case scenario. The destruction might in fact be very localized, limited to merely our own galaxy.
Don't say you weren't warned!
Bill