I don't understand why but it happens all the time in VA getting 87 octane. I used to stop at the Shell in Ashland, VA at exit 92 off RT95 because i was getting the increase mpg there. On my way home i stop at a different exit off RT95 and it was a Exxon and still got approx 2mpg more. Not sure if the station said "May include up to 10% ethanol" but have seen that before on the drive from MA to NC gas station.