I try to be very careful about the quality of fuel I put in my X5. But as far as I know there is only one oil refinery in my local area. Is it possible that this same refinery converts oil to gasoline for Shell, Exxon, Mobil, Chevron, Rotten Robby, and USA Gasoline. In that case its all the same.

All gasoline is basically the same. Many companies pull from one tank. The difference lies in the additive they put into the tanker when they pump the gas. Each company has its own proprietary formula for additives. The better the additive package, the better the gasoline. For my money, the best gasolines are Shell, Amoco, Sunoco and Sheetz. BTW if you have Sheetz in your area, use it in your 4.4 or 3.0 They have a letter from BMW saying that the Sheetz gas meets the BMW standards. If you want to see it, call Sheetz. Good luck,
Serge