Gasoline is largely fungible because it's required by law to be. What can be called gasoline, what additives can (and are required to be) put into it, how much

Gasoline is largely fungible because it's required by law to be. What can be called gasoline, what additives can (and are required to be) put into it, how much energy it has per liter, etc., are all regulated. There was a time where gasoline brands mattered, and the gas you got from Esso might have been slightly different than the gas from Sinclair or Hess or whatever, but that was intentionally regulated into irrelevance because the benefit to consumers of a consistent product was more valuable than allowing brands to differentiate themselves. It took several decades after the widespread adoption of the car (and gasoline as the dominant fuel) for this to happen, and during this time users had to struggle with varying fuels produced from different feedstocks, gumming of engines, dilution of crankcase oil, etc. (This is referred to in period motoring publications as "the Fuel Problem".) The automobile industries and the oil industries basically pointed fingers at each other until the US Bureau of Standards had to step in and mediate on a consistent set of standards that the refiners would produce fuel to, and the engine manufacturers would design their engines against. If this hadn't happened, and the market had been left to sort it out, I suspect you would have ended up having to fill your Ford car only at Sinclair stations, based on some Ford/Sinclair arrangement or whatever. Unfortunately the 'solution' to the Fuel Problem in the 30s involved the introduction of tetraethyl lead, which mars what would have been a good example of mutually beneficial public-private cooperation and useful regulation.