OhioYJ

So my 370 doesn't seem to care which station I use, two vehicles ago I had a Dodge Caliber, that I used to drive back and forth to work. My drive to work is 95% highway, which I just set the cruise and leave it (so it's very consistent, no traffic to speak of).

I found a 4 MPG difference between stations, that was repeatable. I would always do at least two tanks in a row and run them down as low as possible.

23 MPG - BP gas.
25 MPG - Speedway
27 MPG - Shell

I haven't subjected my Z to BP gas, but it doesn't seem to care about Speedway or Shell, gets the same 22.5 MPG no matter what (That's highway by the way too). Well up to 23 MPG now with the Stillen Intake...

Not while it may not be a quality difference, it indicated to me there was a difference.