cases, the committee performed additional technical analyses to fill gaps in the literature or reconcile conflicting assessments. The approaches that the committee used are described in more detail in Part 2 of this report.

The committee also relied heavily on the reports of the three panels that were created as part of this Phase I study to undertake detailed examinations of energy efficiency technologies, alternative transportation fuels, and renewable-energy technologies. The three panel reports are, specifically:

• Real Prospects for Energy Efficiency in the United States (available at http://www.nap.edu/catalog.php?record_id=12621)

• Liquid Transportation Fuels from Coal and Biomass: Technological Status, Costs, and Environmental Impacts (available at http://www.nap.edu/catalog.php?record_id=12620)

• Electricity from Renewable Resources: Status, Prospects, and Impediments (available at http://www.nap.edu/catalog.php?record_id=12619).

The AEF Committee used these panel reports to inform its judgments about energy supply and cost for the particular technologies involved. Selected members of these panels, including their chairs and vice chairs, also served on the authoring committee for the present report.

The U.S. energy system is so large and complex that the committee was unable, in the time available, to assess the potential for transformation of its every relevant aspect. Note in particular that:

• The focus of the report is on energy-supply and end-use technologies that are most likely, in the judgment of the committee, to have meaningful impacts on the U.S. energy system during the three time periods considered in this study (encompassing the next 40 years or so). However, the committee did not assess the future role of technologies for the exploration, extraction, storage, and transportation of primary energy sources (e.g., fossil fuels), nor did it assess the role of some critial components of a modernized infrastructure—including tankers, roads, pipelines, and associated storage facilities—in delivering these resources from suppliers to consumers.

• The report does not explore in any depth the U.S. energy system at the regional level. Thus, the implications of the dramatic regional heterogeneity in the United States—for example, in energy resource endow-