Respectfully disagree. I spent the first part of my career helping refineries around the world safely and efficiently make gas and diesel. There are lots of filling stations, but only so many refineries. Local stations get their fuel supplies from the same handful of regional refineries. It's the same fuel. Each refinery has a terminal for dispensing fuel into tanker trucks, and it's all the same gas and diesel going into those differently branded tankers.
There are some things that do change, though, and that could impact fuel economy and engine health:
1. Winter blend. Refineries have to meet regulations, but the exact day of when they switch between summer and winter blends will vary, and depending on how much stock is left over, changes when it hits a dispenser pump. If one station still has winter blend in their tanks and another has summer blend in their storage tanks, you'll notice a difference in mpg.
2. Ethanol. Ethanol has a lower energy potential, so the more ethanol, the less MPG. How much ethanol is included depends on the station. If one station uses no ethanol and another 10% or 15%, you'll see a difference in mpg.
3. Maintenance and turnover. Station storage tanks and trucks can become contaminated, and if the station has low fuel customer turnover, the fuel can age. It's best to use stations with more traffic for this reason. Keep it fresh.
4. Additives. This is where station brands vary the most. At the terminal where the trucks are filled, the contracts require the refiner to include the additive package advertised by the brand. Chevron Techron as an example. Not all brands have additives. Some have more than others. Costco is one of the best, plain and simple, and it's my first choice for fueling my own vehicles. High customer turnover, well maintained stations and transport trucks, and an impressive additive package. If Costco isn't available or convenient, then I select another brand from the Top Tier list and find a station that sees traffic.
