I had a nightmare yesterday, i dreamt about filling my Z with 87 octane gas from Arco. True story..

I have no idea how it is calculated, but I never trust these gauges. I wouldn't even consider them to be "rough" estimates. I just do the math on my phone at every fill up. :tiphat:

wow.. i had no idea different types of gas made such a big difference in mileage o.O. kinda makes me want to test out this claim. but i'd say stick with cheveron and shell !!

I have not notice any difference in mpg's when using ARCO, Shell, Chevron?

Actually if the gas brand did make a mpg difference don't you think they would promote that.

Maybe I just got a particularly bad batch. I filled up with 76 after I got to half on that Arco tank a week ago and I am now back to a more normal mileage. 180 miles on a half tank vs less than 130 on the last one. I agree it seems to drastic of a difference to be the norm, but I'll still stay away from Arco from now on.

I've had mileage drop by 5-6, and I always get gas from the same place. I've always just wrote it off as a fluke.

Shell or Chevron unless I'm running on fumes.

did I accidentally click a link to a a prius forum?

Honestly though isn't this about the time that most gas stations switch over to "winter gas"? I thought winter blends of gasoline typically give lower mpg.