and what EXACTLY do you mean by "unbranded gasoline"
i can only speak to my area, but i'm sure others are no different, but around here, ALL the Gasoline sold, regardless of the "brand" on the pump, comes from the Local Husky Refinery.
they make 25% of the gas sold in the state of Ohio.
every single tanker goes out to the Fuel Depot (right next to the refinery, but IIRC run by Marathon) and fills with the same gas, plus their companies "secret sauce" of additive cocktails.
same was true whether the refinery was owned by Standard Oil, SOHIO,BP, Clark, Valero, and now Husky....