something I learned yesterday from a arson investigator...gas stations 90% of the time either have too much gas being delivered or not enough to make it through the day. It is very common for them to share gas, and since their tanks are so big, most of the time it is not filled with one "brand" of gas. This is also why when they investigate arson where gas is involved, they cannot determine which station it came from.
With that being said, I would stay away from the small stations because they are looking for the cheapest thing they could find at the time, but for the rest of the big companies, there really is no difference from one to the next.
Another gas station tip is to get to know someone that works there.
A lot of times they only order premium and fill all of the tanks with it. If their quantity discount make sit chepaer than regular, they do that then if you know someone there, they can tell you when to pay for regular and get premium.
My girlfriend has been getting terrible mileage in her truck. She's been driving a dodge dakota while her Firebird is in the shop, and she was getting about 180 a tank. She always bought gas from this little dinky store.
She got gas at a good station the other day, and got 280 to the tank!
Chevron, Texaco, or BP. All gas is the same, they just have different additives (techron). I talked to a gas tanker driver and he said he gets the gas from the same place and delivers to most all of the main plants. Only thing they do is add something to it to make it their own.