Ethanol is a biofuel that when in anhydrous form - when it contains 1% water or less - can be blended with gasoline in varying concentrations. Use of ethanol has two primary benefits; reduced consumption of petroleum fuels and diminished greenhouse gas emissions.
Dependence on foreign oil is a frequently cited security concern. Ethanol use limits this dependence as it can be produced in abundance in North America. Furthermore, as a renewable resource that is produced from plantlife, it has a replenishable supply, unlike petroleum which is finite and exhaustible.
The burning of petroleum based fuels is also the largest source of greenhouse gas emissions. According to the University of Chicago's Argonne National Laboratory the use of 10% ethanol blends reduces greenhouse gas emissions by 18-29% when compared with conventional gasoline. According to the USDA, the return on every unit of energy invested in producing ethanol is 1.67 units.
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