Originally Posted By: Trav
It doesn't. One is a synthetic GTL base stock with very low NOAK and outstanding cleaning abilities, the other is primarily GP III with higher NOAK, just run of the mill stuff like PP or the others (not that there is anything wrong with them, they are all decent).
PU is Shell's premium product for the US Market.
Thanks for the explanation, I'm running PU now and love it.
I heard QSUD was made by Shell as well but I'll be sticking to PU.