Ever notice the meters on gas pumps that roll as the gas is pumped to show how much is going out. I noticed at sunoco they have a low and a high. I pumped 91 the other day and both the low and high roll. However when pumping 93 only the high gauge does. I remenber reading about sulpher levels in different companies and grades. With sunoco it was basically the same until u hit 93 or 94. Guess I know why 91 was no better than 87 in that aspect atleast. I've read on here, and elsewhere that bp/amoco uses a extra refining step on their ultimate 93. I wonder if sunoco does something similar.