Guys:

Exclude California from anything I say later in this post. CARB rules are very demanding! Also, Exxon here is only used as an example. I have no connections, personal, financial or professional with Exxon.

The Gasoline Distribution system in the US relies on pipelines. Colonial pipeline goes from Houston to (essentially) New York, with termials along the way. A refiner puts it's gas in at Houston (say 25K bbls) and let's say it pulls it out at a terminal in New Jersey. IT'S NOT THE EXACT SAME GASOLINE THAT IT PUT IN! So, while you may want to buy Exxon gasoline, you may be getting gasoline that was made by Shell, or Phillips or BP. Gasoline is a Fungible Commodity (or else it couldn't be sold on the NY Merc).

NOW comes the fun part. At that terminal in New Jersey, if you're say Exxon, when you pick up the gasoline in your truck to deliver it to your Exxon station on Route 9, you add your own proprietary additives. THIS IS WHAT MAKES IT EXXON GASOLINE.

Essentially all gasoline is the same in the US (with the aforementioned Califronial exception AND the EPA designations of Reformulated (RFG) and Conventional (CG)). (Remember that Unocal got some moron Judge in Cali to allow it a patent on RFG - it was overturned years later) This allows it to be distributed to folks in Rhode Island where there isn't a refinery close by (unless you count the Irving Refinery is St. John, New Brunswick).

What makes Exxon gasoline Exxon gasoline is 1) their internal quality control at the terminal and 2) their proprietary additives. If you ask over on the Corvette forum, they would generally recommend Chevron gasoline.

Personally, I only buy from Exxon, Chevron, BP and Shell stations. Additives and quality control. I don't ever by from a convienence store or Costco or Kroger.

Just my 2 cents.

Ole Joe