Pros of ethanol-supplemented fuel:

•Ethanol is clean-burning and is a higher-octane fuel than conventional gas.
•Ethanol is produced from renewable sources.
•Ethanol-powered vehicles produce lower carbon monoxide and carbon dioxide emissions, and lower levels of hydrocarbon and nitrogen oxide emissions.
•Ethanol production keeps American farmers in business and creates new farming and ethanol-processing jobs.
•Because ethanol is produced domestically, it reduces U.S. dependence on foreign oil and increases the nation’s energy independence.
•Ethanol needs fewer fossil (coal) and petroleum (gas) fuels to produce more BTU of energy than gasoline (although it does require much more water).

Cons of ethanol-supplemented fuel:

•Ethanol creates 34 percent less energy than unadulterated gasoline per gallon. This equals a loss in fuel economy of up to 3 miles per gallon for E10 fuels. In terms of heat, ethanol produces 76,330 BTU per gallon, whereas diesel fuel produces 128,450 BTU per gallon, gasoline 116,090 BTU per gallon and LP gas 84,950 BTU per gallon. The fuel economy gets even worse with E85, a loss of 7 to 8 miles per gallon with its higher ethanol content. Consumer Reports, testing in 2006, verified a loss in fuel economy of up to 30 percent in a Chevy Tahoe designed to run on flex fuel when it was tested with both unleaded gas and E85. Poor fuel economy can also be attributed to improper fuel system calibration based on computer feedback from oxygen sensors because of the temperatures needed to burn ethanol.
•Virtually any grain considered feedstock can be used to make ethanol, but some grains are better for producing ethanol than others. Corn happens to be one of the worst grains for making ethanol but we produce so much more of it than any other grain that it was the ingredient of choice for U.S. ethanol producers. In South America, ethanol is produced from sugar cane, which is easier to refine and gives a higher yield per acre than corn (1,200 gallons per acre vs. 300 gallons per acre of corn). The U.S. government did impose a 55 cents per gallon tariff to prevent the import of sugar cane-based ethanol into the United States, though that tariff has recently expired).
•Ethanol is hygroscopic, which means it absorbs water more easily than gasoline. That leads to water condensation inside fuel tanks, carburetor fuel bowls and fuel lines where air spaces are present. Water content in fuel will also swell up the paper filter media inside fuel filters not specifically designed for flex fuels and can thus restrict fuel flow at the filter.
•Ethanol also erodes fiberglass tanks, rubber hoses and plastic fuel lines. It contributes to rust in fuel systems by creating condensation in the unfilled portion of gas tanks. It will also dissolve varnish and rust in steel fuel components. These dissolved ingredients sit in the bottom of gas tanks until they are removed or they will enter the fuel system if the fuel level in the tank gets too low.