Ethanol gas is a type of fuel that contains ethyl alcohol, the same type of alcohol found in alcoholic beverages. It is most commonly used as a biofuel additive for gasoline, and more than 98% of U.S. gasoline contains ethanol to oxygenate the fuel. Ethanol is a renewable fuel made from various plant materials collectively known as "biomass".

Here are some key facts about ethanol gas:

• Ethanol is available in several common fuel mixtures, including E10 (10% ethanol, 90% gasoline), E15 (10.5% to 15% ethanol), and E85 (flex fuel), which can be used in flexible fuel vehicles designed to operate on any blend of gasoline and ethanol up to 83% .
• Ethanol has a higher octane number than gasoline, providing premium blending properties. Minimum octane number requirements for gasoline prevent engine knocking and ensure drivability. Lower-octane gasoline is blended with 10% ethanol to attain the standard 87 octane.
• Ethanol is a particulate-free burning fuel source that combusts with oxygen to form carbon dioxide, carbon monoxide, water, and aldehydes. The Clean Air Act requires the addition of oxygenates to reduce carbon monoxide emissions in the United States. The additive MTBE is currently being phased out due to groundwater contamination, hence ethanol becomes an attractive alternative additive.
• Ethanol is hygroscopic, meaning it absorbs water vapor directly from the atmosphere. Because absorbed water dilutes the fuel value of the ethanol and may cause phase separation of ethanol-gasoline blends (which causes engine stall), containers of ethanol fuels must be kept tightly sealed.
• Ethanol is not efficiently shipped through modern pipelines, like liquid hydrocarbons, over long distances because of its high miscibility with water.

In summary, ethanol gas is a renewable fuel made from plant materials that is commonly used as a biofuel additive for gasoline. It has a higher octane number than gasoline and is a particulate-free burning fuel source. However, it is hygroscopic and cannot be efficiently shipped through modern pipelines.