[bodyfour]

> Apparently our mid-grade is a 50/50 mix of regular and high-grade. I don't know if that makes sense, but that is what I've been told by 4-5 different people.

Yes, typically gas stations only have two tanks of gasoline: low-grade and high-grade. When you select mid-grade it's blended at the pump.

[ovi256]

Given that the difference between low and high octane is the proportion of two different hydrocarbures, blending them to get mid-grade fuel sounds ok.