from fuel-cell-powered vehicles would be water vapor, and America would drastically reduce its dependence on foreign fuel supplies.

There are several significant obstacles to achieving that vision. Present fuel cells are too expensive and unreliable for the mass market. And hydrogen is very difficult to store and transport in a vehicle unless it is compressed to thousands of pounds per square inch (psi). Automotive companies are using containers in their demo vehicles that can store hydrogen at 5,000 to 10,000 psi, but a cost-effective and safe distribution system would have to be put in place before these vehicles could become widely available.

Furthermore, hydrogen (like electricity) is not a primary source of energy but rather an energy carrier. There are no natural reservoirs of pure hydrogen; it must be extracted from compounds such as natural gas or water. And the processes for separating it from these principal sources pose their own challenges. When natural gas (basically methane, a lightweight molecule made of carbon and hydrogen) is exposed to steam under high temperatures in the presence of a catalyst, it frees the hydrogen. However, the process itself also produces substantial amounts of CO2. Widespread use would require a carbon sequestration scheme. And, of course, hydrogen can be extracted from water by electrolysis. But that takes a lot of electric power. So unless the electricity is generated by nuclear or renewable sources, the environmental advantage of hydrogen is substantially negated.

The federal government, particularly the U.S. Department of Energy, is conducting significant research on fuel cells to accelerate their development and successful introduction into the marketplace. And hydrogen-fuel-cell cars are receiving considerable attention in the press. Some car manufacturers, including General Motors and Honda, are putting a very limited number of these vehicles on the road. There are hydrogen fueling stations in about 16 states, the greatest number being in California. Most of these, though, are small, private facilities intended to support a few experimental vehicles. It will take decades of research and development, as well as changes in the energy infrastructure, before a hydrogen economy on a broad scale can be achieved.


There are several “unconventional” petroleum sources, materials from which oil can be extracted—at a cost. Resources are abundant and could greatly impact the U.S. oil supply in the future. The three largest are oil shale (rock that releases petroleum-like liquids when heated in a special chemical process); tar sands (heavy, thick, black oil mixed with sand, clay, and water); and heavy crude oil (thicker and slower flowing than conventional oil).

The most extensive deposits of all three are in North and South America. A region covering parts of Colorado, Utah, and Wyoming contains oil shale

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement