totaling about three times the proven oil reserves of Saudi Arabia. About two-thirds of the world’s supply of tar sands (estimated at 5 trillion barrels, though not all of it is recoverable) is found in Canada and Venezuela. Venezuela also has the largest known reserves of heavy crude oil, estimated at 235 billion barrels.


However, extracting these resources is much more costly, energy intensive, and environmentally damaging than drilling for conventional oil. The processes by which we mine and refine oil shale and tar sands to produce usable oil, for example, involve significant disturbance of the land, extensive use of water (a particular concern in dry regions where oil shale is often found), and potential emissions of pollutants to the air and groundwater. In addition, more energy goes into these processes than into extracting and refining conventional oil, and more CO2 is emitted. But as conventional oil costs rise, more attention is being focused on alternative sources and on overcoming the challenges associated with their use. Canada already produces more than a million barrels per day of oil from tar sands, and some companies are interested in pursuing oil shale in the United States, probably using below-ground techniques to extract the oil without mining the shale.

BIOFUELS

Fuel derived from plant material, or biofuel, is an appealing renewable alternative to fossil fuels. It is uncertain, though, whether biofuels are ultimately viable in the absence of subsidies. In particular, the prospects for “biodiesel” fuel—a relatively heavy liquid derived from soybean, vegetable, rapeseed, or safflower oils, among others—are considered doubtful. Typically, those oils are already expensive compared to fossil-fuel sources, and there does not appear to be a way to bring the cost down.

As mentioned previously, corn-based ethanol is already offsetting a small amount of fossil-fuel use in vehicles. However, many experts believe that ethanol-based biofuels will not provide much benefit until the conversion technology is fully developed to use cellulose (as found in trees and grasses) for the raw material instead of corn or sugar cane. In fact, the Energy Independence and Security Act of 2007 stipulates that by 2022 the United States must produce 21 billion gallons of advanced biofuels, such as cellulosic ethanol. Research is under way in this field, which could provide a ubiquitous sustainable resource and perhaps take advantage of the existing nationwide infrastructure created for petroleum-based fuel distribution.


Even with this increased focus on biofuels, however, it is uncertain how much projected gasoline consumption can be replaced in the next few decades. Furthermore, biofuels contain carbon, and although they may burn “cleaner” than oil-derived fuels, they would not completely eliminate CO2 emissions.


Many of these technologies will likely contribute in some way to America’s energy sources in the 21st century. But it is impossible to predict how much impact these and other technologies will have on our energy future.



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