Alternative fuel, also known as non-conventional fuel, is any material or substance, other than petroleum, which is consumed to provide energy to power an engine. Some alternative fuels are biodiesel, ethanol, butanol, chemically stored electricity (batteries and fuel cells), hydrogen, methane, natural gas, wood, and vegetable oil. The need for the development of alternative fuel sources has been growing, due to concerns that the production of oil will no longer supply the demand.
   Alternative fuel has become a topic of rapidly increasing interest due to global warming, rising gasoline prices, and the increasing pressure put on crude oil stocks. In the year 2000, there were about eight million vehicles around the world that ran on alternative fuels, indicating their increasing popularity.

Renewable Energy

A possible solution to a potential future energy shortage would be to use some of the world's remaining fossil fuel reserves as an investment in renewable energy infrastructure such as wind power, solar power, tidal power, geothermal power, hydropower, thermal depolymerization, methanol, ethanol and biodiesel, or in an oil lamp; try olive oil, canola oil, safflower oil, or sunflower oil which do not suffer from finite energy reserves, but do have a finite energy flow. The construction of sufficiently large renewable energy infrastructure might avoid the economic consequences of an extended period of decline in fossil fuel energy supply per capita.
   Most alternative fuels assume a source of renewable energy or at least sustainable energy (such as nuclear power) as a source of the fuel. A few alternative fuels (for example, hydrogen) may be made by sustainable or nonsustainable means. If they are made by non-sustainable means, such fuels are offered as alternatives usually because they offer to cause less pollution at the point of use, and perhaps less pollution overall.

Non-conventional oil

Non-conventional oil is another source of oil separate from conventional or traditional oil. Non-conventional sources include: tar sands, oil shale and bitumen. Potentially significant deposits of non-conventional oil include the Athabasca Oil Sands site in northwestern Canada and the Venezuelan Orinoco tar sands. Oil companies estimate that the Athabasca and Orinoco sites (both of similar size) have as much as two-thirds of total global oil deposits, but they are not yet considered proven reserves of oil.
   Extracting a significant percentage of world oil production from tar sands may not be feasible. The extraction process takes a great deal of energy for heat and electrical power, presently coming from natural gas (itself in short supply). There are proposals to build a series of nuclear reactors to supply this energy. Non-conventional oil production is currently less efficient, and has a larger environmental impact than conventional oil production.

Other fossil fuels

It is expected by geologists that natural gas will peak 5-15 years after oil does. There are large but finite coal reserves which may increasingly be used as a fuel source during oil depletion. The Fischer-Tropsch process converts carbon dioxide, carbon monoxide, and methane into liquid hydrocarbons of various forms. The carbon dioxide and carbon monoxide are generated by partial oxidation of coal and wood-based fuels. This process was developed and used extensively in World War II by Germany, which had limited access to crude oil supplies.
   It is today used in South Africa to produce most of that country's diesel from coal. The Karrick process is an improved methodology for coal liquefaction, with higher efficiency. Since there are large but finite coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to become scarce.

Nuclear power and transportion energy and fuel

The U.S. would require at least an eightfold increase in nuclear power production, from 10% of all energy supplied to about 90%, to replace both the current amount of electricity generated from fossil fuels and gasoline usage.

Fission reactors

Nuclear engineers estimate that the world could derive 400,000 quads (quadrillion, 1015, British thermal units), or about 420,000 EJ (exojoules = 1018 joules), of energy (1000 years at current levels of consumption, assuming new technology) from uranium isotope 235, if reprocessing is not employed. As uranium ore supplies are limited, a majority of this uranium would have to somehow be cost-effectively extracted from seawater. But, this technology does not exist. However, at the current technology and consumption, the reserves will last 50 years.
   Fast breeder reactors are another possibility. As opposed to current LWR (light water reactors), which burn the rare isotope of uranium U-235 (producing and burning about an equal amount of plutonium in the process), fast breeder reactors produce much larger amounts of plutonium from common U-238, then fission that to produce electricity and thermal heat.

Fusion reactors

It is relatively easy to start nuclear fusion reactions, which generate large amounts of energy (such as nuclear weapons). However, the energy input needed in achieving the necessary temperature and electromagnetic confinement for controlled and sustained fusion is too large presently to maintain a significant energy gain.
   Electricity produced in a typical fusion facility would not involve the creation of millenary radioactive waste, neither would it involve a risk of nuclear meltdown. The natural resources required for the implementation of the DT (Deuterium-Tritium) fuel cycle (the option that is most likely to be put into effect) are essentially inexhaustible.

Hydrogen

Proponents of a hydrogen economy think hydrogen could hold the key to ongoing energy demands. Relatively new technologies (such as fuel cells) can be used to efficiently harness the chemical energy stored in diatomic hydrogen (H2). However, there is no accessible natural reserve of uncombined hydrogen (what there is resides in Earth's outer exosphere) and thus hydrogen for use as fuel must first be produced using another energy source; hydrogen would thus actually be a means to transport energy, rather than an energy source, just as common rechargeable batteries are.
   The most immediately feasible hydrogen mass production method is steam methane reformation, which requires natural gas, itself potentially in increasingly short supply. Another method of hydrogen production is through water electrolysis which can use electricity generated from any combination of: fossil fuels, nuclear, and/or renewable energy sources. Biomass or coal gasification, photoelectrolysis, and genetically modified organisms have also been proposed as means to produce hydrogen.