[SkiSmuggs]

Diesel fuel is not always made by the brand that sells it, nor is gasoline. I talked to a tanker driver who left an Irving station and went to a Mobil station. He said Irving refines it and supplies it as Mobil has no refining plants in New England. He said there are no additive added at either location, it is just what he delivers. Gas is similar for the base product, but each station has the brand name additive package.
Top Tier gasoline has a real advantage over non-TT as in has a lot more detergents, etc. Tests have shown better mileage and cleaner engine parts and may be worth any small extra cost in both fuel and maintenance savings according to independent studies.
It is the engine manufacturers who asked for the Top Tier fuels for better performance, mileage and longevity.