<P> The principle of supply and demand holds that as hydrocarbon supplies diminish, prices will rise . Therefore, higher prices will lead to increased alternative, renewable energy supplies as previously uneconomic sources become sufficiently economical to exploit . Artificial gasolines and other renewable energy sources currently require more expensive production and processing technologies than conventional petroleum reserves, but may become economically viable in the near future . Different alternative sources of energy include nuclear, hydroelectric, solar, wind, and geothermal . </P> <P> One of the more promising energy alternatives is the use of inedible feed stocks and biomass for carbon dioxide capture as well as biofuel . While these processes are not without problems, they are currently in practice around the world . Biodiesels are being produced by several companies and source of great research at several universities . Some of the most common and promising processes of conversion of renewable lipids into usable fuels is through hydrotreating and decarboxylation . </P> <P> The United States holds less than 5% of the world's population, but due to large houses and private cars, uses more than 25% of the world's supply of fossil fuels . As the largest source of U.S. greenhouse gas emissions, CO2 from fossil fuel combustion, accounted for 80 percent of (its) weighted emissions in 1998 . Combustion of fossil fuels also produces other air pollutants, such as nitrogen oxides, sulfur dioxide, volatile organic compounds and heavy metals . </P> <P> According to Environment Canada: </P>

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