David and Goliath
In order to produce half the motor fuel used in the US today, it would require a tripling of the current production of corn. (Corn required for 50% US Motor Fuel Approx 700 mmt = 70 bil gals)
Ethanol fuel has less Btu energy content, which means it will consume more fuel to cover the same distance. The more-expensive premium fuel contains low or no ethanol. In high-compression engines, low ethanol content, slower-burning premium fuel is required to avoid harmful pre-ignition (knocking). Very-expensive aviation gasoline (Avgas) is 100 octane made from 100% petroleum. The high price of zero-ethanol Avgas does not include taxes.
Ethanol is highly corrosive to fuel systems, rubber hoses-and-gaskets, aluminum and combustion chambers. Therefore it is illegal to use fuels containing alcohol in aircraft. Ethanol is incompatible with marine fiberglass fuel tanks, which make them leak. For higher ethanol percentage blends, and 100% ethanol-run vehicles, modifications to the engine is required.
Corrosive ethanol cannot be transported via petroleum pipelines, therefore stainless steel tank trucks are used in road transportation. However this increases the overall cost and energy consumption required to deliver ethanol to the customer at the pump.
Many car manufacturers are now producing flexible-fuel vehicles (FFV's), that can safely run on any combination of bioethanol and petrol, up to 100% bioethanol. They dynamically sense oxygen content from the exhaust, and adjust the engine's computer systems, spark, and fuel injection accordingly. This increases the initial cost and vehicle maintenance fees. When FFV system maintenance is needed but not performed, the efficiency falls and pollution emissions increases. FFV internal combustion engines are becoming increasingly complex which impacts cost, maintenance, reliability and also, useful lifetime longevity.
Alcohol mixes with both petroleum and water, so ethanol fuels are often diluted by moisture absorbed from the environment after the drying process. Alcohol-mixed fuels containing water reduces efficiency, as it makes engines harder to start, causes intermittent operation (sputtering), and also oxidizes aluminum (carburetors) and steel components (rust).
Dry ethanol has roughly one-third lower energy content per unit of volume when compared to gasoline, therefore larger fuel tanks or more fuel stops are required for the same energy content. With large non-sustainable and non-scalable subsidies, ethanol fuel will still cost much more per unit of distance travelled than the current gasoline prices.
Studies have been done to calculate energy balance for biofuel production. Some of these results show large differences depending on the where and what biomass feedstock is used.
One specific example would be a June 17, 2006 editorial in the Wall. St. Journal stated, "The most widely cited research on this subject comes from Cornell's David Pimental and Berkeley's Ted Patzek. They've found that it takes more than a gallon of fossil fuel to make one gallon of ethanol 29% more. That's because it takes enormous amounts of fossil-fuel energy to grow corn (using fertilizer and irrigation), to transport the crops and finally to turn them into ethanol."