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Ethanol fuel - Wikipedia:

For ethanol to contribute significantly to transportation fuel needs, it would need to have a positive net energy balance. To evaluate the net energy of ethanol four variables must be considered: the amount of energy contained in the final ethanol product, the amount of energy directly consumed to make the ethanol (such as the diesel used in tractors), the quality of the resulting ethanol compared to the quality of refined gasoline and the energy indirectly consumed (in order to make the ethanol processing plant, etc).