Biodiesel
Biodiesel is a low-polluting diesel alternative that can be made from vegetable oils, animal fats, and even recycled cooking greases. The health effects of biodiesel are low, its emissions are low, and it's biodegradable.

Electricity
Electricity is considered a fuel when used in electric vehicles. Electricity as a fuel shifts the burden of pollution control to the electrical supply systems, resulting in much lower emissions per mile traveled.

Ethanol
Mainly used today as a fuel additive (see Improved Petroleum-Based Fuels), ethanol is also used in an 85-percent-ethanol/15-percent-gasoline blend, called E85. The main technical goals are to lower the cost of ethanol while expanding the ethanol infrastructure. Currently, the industry is supported by various fuel standards, codes, and legislation.

Hybrid
Hybrids are vehicles that combine an internal combustion engine with an electric motor as the power source. Hybrids utilize the electric motor and battery storage to maximize the fuel economy from standard gasoline-burning engines. Depending upon the design and usage, hybrids can boast up to 30 percent fuel savings (sometimes more) over a comparable gasoline vehicle.

Hydrogen
Although hydrogen can fuel an engine directly, or serve as a fuel additive, the current emphasis is on the use of hydrogen to supply fuel cells, which power electric vehicles. Hydrogen has also been blended with methane to form a fuel called Hythane.

Natural Gas
Natural gas is a clean-air alternative to conventional fuel. It is used in vehicles as compressed natural gas (CNG) or liquefied natural gas (LNG). There are limited fueling sites for natural gas.

Propane
Propane is usually used in the form of liquefied petroleum gas (LPG). Again, the availability of refueling sites is an issue for vehicles that run on this fuel.

P-series
P-series fuels are new fuels that are now classified as an alternative fuel. The fuels are blends of methyltetrahydrofuran (MTHF), ethanol and hydrocarbons. The fuels contain at least 60 percent non-petroleum energy content derived from MTHF (manufactured solely from biomass feedstocks) and ethanol.