The use of ethanol as a fuel for internal combustion engines, either alone or in combination with other fuels, has been given much attention mostly because of its possible environmental and long-term economical advantages over fossil fuel.
Ethanol fuel is an alternative to gasoline.
It can be combined with gasoline in any concentration up to pure ethanol (E100).
Anhydrous ethanol, that is, ethanol without water, can be blended with gasoline in varying quantities to reduce the consumption of petroleum fuels, as well as to reduce air pollution.
In the US, tolerance of ethanol depends on the individual vehicle.
In Brazil, ethanol-powered and flexible-fuel vehicles are capable of running on hydrated ethanol, an azeotrope of ethanol and water.
In addition, flexible-fuel vehicles can run on any mixture of hydrated ethanol and gasoline, as long as there is at least 20% ethanol.
A few flexible-fuel systems, like the Hi-Flex, used by Renault and Fiat, can also run with pure gasoline.
Ethanol is increasingly used as an oxygenate additive for standard gasoline, as a replacement for methyl t-butyl ether (MTBE), the latter chemical being responsible for considerable groundwater and soil contamination.
Ethanol can also be used to power fuel cells and to produce biodiesel.