..i've noticed around a -1mpg difference using gas from the generic (aka. mom-&-pop) Raceway station, rather than using my usual RaceTrac station for fill-ups..RaceTrac is "name brand" down here in Texas (dunno about where you reside)..
..anyhow, let's consider a 15gal gas tank & a 5cent/gal price difference between a no-name station (say $1.50/gal) & a branded one ($1.55/gal)..
..if the cheaper gas gets you 20mpg, you'll fill your tank at a cost of $22.50 & roll 300 miles..that's a cost-per-mile of $0.075..if the branded gas gets you 21mpg, you hit 315 miles to the tank & the fill-up costs $23.25..that calc's to $0.738/mile..
..obviously, you're paying less-per-mile with a 1mpg increase, even if you spend 5cent/gal more..
..however, if there's a 10-cent/gal price differential, the branded gas ends up costing you $0.762/mile (again, provided you get the 1mpg boost from the more costly gas)..cheapie gas outweighs a 1mpg performance increase, in this case..
..it looks like, at a 7cent/gal difference ($1.57 in our example), your cost-per-mile is $0.748, which is slightly better than the $1.50/gal no-name gas performance (but just barely)..
..i think my point is that you should eval your MPG results on a station-by-station basis..put 2-3 tanks in your ride & monitor the MPG results..if you perceive a significant dip, then realize paying up to 7cents/gal less isn't really saving you anything, if your overall MPG is 1mpg or better than you get from the gas at another station..
..furthermore (& pls note: i don't have the brain cells left to figure this point out fully, right now), don't forget that if you have to travel significant miles (i think i figured it as a 15-mile round-trip for 2-to-3cents less per gallon, one time) to actually REACH cheaper gas, then it's not economically intelligent to travel said distance for the cost-difference..(ie. it doesn't make sense to drive 20miles one-way to sit in line for $1.30/gal gas, since the travel & idle time will effectively kill any $-savings you were expecting)..
..my conclusions (and please (PLS) feel free to critique, correct, and/or extrapolate, as ya see fit)..if you get +1mpg using "better" fuel, you shouldn't go to any station that's selling for 7cents/gal or less than a "reliable" supplier..
..again, it requires that you monitor each station you fill-up at for (i'd say) a minimum of 3 tank-ups..if you see lesser results from a certain station, then infrequent them (to turn a term)..i'm now infrequenting the Raceway i was filling up at because RaceTrac is simply giving me better results (at about a 2cent/gal price difference)..
just some thoughts..
(owner of T'Pal; Subaru Legacy Outback)
The quality of the gas is important, so is the ethanol content. Back about 20 years ago when So Cal Air Quality Managment outlawed tetraethyl lead in motor fuels ARCO (Atlantic Richfield Corp) started adding alcohol to their gas and calling it EC1 and pumping it out of the old leaded gas dispensers. Up to that point I used to buy a lot of ARCO gas for my unleaded burning 1988 Acura Integra and had good results with it along with a savings of about 3 cents per gallon since ARCO didn't accept credit cards and charged a cash only price. The car ran fine on it and I never observed any decrease in performance or mileage with the ARCO gas over more name brands sold at higher costs (remember that in that era gas was running at just under $1.00 a gallon in my area). When ARCO switched to the alcohol blend to meet the lead ban, I noticed a decrease in mileage from my car along with finding that it had fouled a fuel filter for the first time in its' life. I switched to Unocal 76 (Conoco / Phillips 66 now) and regained my mileage and drove for the next 135,000 miles without having to replace another fuel filter. My point is that I agree with you, I paid an extra $0.03 - 0.05 a gallon for gasoline and didn't suffer the performance loss, mileage decrease, and fuel system problems that the alcohol infused gasoline caused. It was a much better deal to spend a few cents more per gallon. To this day I'm careful about what gasoline I put into my vehicles. My wife's last car was a 1998 Chevy S-10 Blazer with the 4.3 liter V-6 Hi Per engine and towing package. That car had trouble with the fuel injection poppets sticking. After having them replaced on 3 different occasions Chevy finally sent out a letter to all owners with that model of engine along with the 5.0 and 5.7 liter V-8s that Southern California Chevron (Standard Oil) gasoline had some sort of additive that was causing the poppets to stick and suggesting that all owners cease and desist from putting that fuel into their vehicles. When my wife switched to Exxon / Mobil gasoline after that she never had another fuel injection problem with that car. So it isn't just the off brand fuel, but sometimes even the name brand fuels can have additives that are harmful or at least problematic for an individual engine application. Stick with what works for you and don't quibble over a few cents per gallon you may end up getting much more than that back in increased mileage or decreased maintenance costs for your vehicle.
Another fun note to the gas staion grades is the oil carriers do somesort of measurement (I wish I could remember what the guy said) of when they are filling up there trucks. Oil settles in tanks, kind of like if anyone has had a Black and Tan Beer, Guniess and Bass ale, the two will seperate in a glass much like diffent oils. they can take out the top part or the bottom part at any time. Thus seperating what they have in the tank. I think that process is also how they seperate the different parts of a barrel of oil. they process it and then pull what they want off of it. heavy stuff on the bottom, lighter stuff at the top. I would think diesel is heaver and gas I think it lighter. There is a diagram somewhere on the net that will let you know what they actually get out af a barrel of oil. From Avation to gear oil. I just like the the Black and Tan beer way of thinking! LOL!