I dont think it will matter what or where the fuel come's from the price and amount of miles per gallon are both set by government tax and the oil companies.
15 years ago I worked as a test driver for a well known oil company, we had a fleet of 6 diesel cars, 3 of which were fuelled from forecourt pumps and the other 3 fuel from drum's all cars were driven over a 410 mile road course per shift.
The cars fuelled from the forecourt would return between 40 to 50 mpg pretty much what you would expect, the cars fuelled from the drums which was diesel with additives would return around 90 mpg, and this was 15 years ago when the cars were not as efficient as modern diesels.
All the cars were 1.8 litre turbo diesel saloons and estates.
Where is the incentive for the fuel companies to market and sell these fuels at the end of the day they would sell half the fuel
and could probably only justify a small increase in the cost at the pumps.
I would prefer a full bottle in front of me than a full frontal lobotomy.
Seek not excess, God hates he who roams !