The United States now stands at a critical juncture in the evolution of its energy policy, particularly with respect to petroleum and natural gas consumption. The demand for energy in this country has been rising steadily over the past years as a result of continued economic growth and the vital role of air, ground, and sea transportation in all aspects of economic activity. According to the U.S. Department of Energy (DoE), total energy use in the United States grew by 16 percent between 1990 and 2002, and is projected to grow by another 35 percent between 2002 and 2025. At the same time, many other countries, both developed and developing, have also experienced an increased need for energy, pushing total world energy use from 348 quadrillion BTUs in 1990 to a projected 645 quadrillion BTUs in 2025, an increase of 85 percent.