does brand of fuel affect milage, just switched brands and milage went up by 3mpg

[olpos]

i find it very hard to believe, but it did happen on two cars so far.
after many fill ups at the chevron just around the corner both of my cars got around 17mpg.sometimes 18mpg. yes a lot of around town, short freeway trips at 80 mpg. my guess is 40- 50 fill ups at chevron(premium only) i check milage at every fill up. i swiched to arco premium almost 2 months ago(cheapest name brand down here)and got an even 20mpg. at first i thought it was just better driving? using arco only both cars have stayed at 20mpg, 19.9 last check. this car sees 80-95 mph almost daily the same is true of the 190e. a 3mpg increase with no tune or change of driving habit is very hard to believe, and on two cars.
has anyone else had this happen to them
rich

It sounds more like your old filling stations pumps were innacurate, and overcharging you. All of the gasoline brands get their fuel from the same distribution points, and add their additive packages to their fuels, after receiving their requisite quantities of fuels. In effect, you are pumping the exact same stuff that Shell, Conoco, Diamond Shamrock, BP, and Joe Schmuckarellies mom and pop down the block is selling.

I would take a couple of 5 gallon gas cans, mark a verified, measured level for 5 gallons. Go to both stations. The first place will either come up short at 5, or the Arco will pump more than the indicated quantity on the pump.

[420SEL]

I have tracked my gas mileage by station, gas company and type of driving for over 5 years. I have definitely found a difference in mileage by gas company. I now stick with one company.

[olpos]

thanks for the replys. i do know that the fuel is all the same till they add fuel adatives to turn it into thier brand . also for making premium from regular
i use differant pumps at these stations, so i think it's not a bad pump reading. i will try some more experiment's but this has me looking now.
thank you
rich