Yes but it's not less efficient. Maybe this chart will help explain? Different fuels contain different amount of energy per gallon. Your only looking at MPG and not fuel efficiency. Think about why Diesel gives better fuel mileage? It's because Diesel contains more energy per gallon.

From the above chart;

Diesel has 128,000-138,000 BTU/Gal

Gasoline has 112,000-120,000 BTU/Gal

Ethanol only has 76,330-84,530 BTU/Gal

Methanol only has 57,250-65,200 BTU/Gal

As you can see this is exactly what happens in real life. Diesel gives the highest MPG BECAUSE it has the highest energy per GALLON. Then gasoline and then Ethanol and finally Methanol.

It's all about the energy density of the fuel.

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