extraction and use of fossil fuels entail growing security, economic, and environmental risks. A crucial question, therefore, is whether this existing energy infrastructure can be supplied with liquid, gaseous, and solid fuels in the future at acceptable levels of such risks. If so, much of it can remain in place. If not, the embedded capital stock of technologies for energy production and use will need to change through a combination of market forces and policy choices.

Other chapters of this report discuss alternative pathways for providing the energy services that modern society demands. For example, the chapter on alternative transportation fuels (Chapter 5) provides an assessment of the technologies and environmental impacts of liquid fuels derived from biomass feedstocks, coal, or natural gas. This present chapter focuses on alternative ways of using fossil fuels to serve the existing energy-use infrastructure. Specifically, it explores:

• The extent to which the U.S. endowment of fossil fuels is limited in its ability to meet future needs for liquid, gaseous, and solid fuels by means of conventional pathways.

• New technologies that may become available for producing the desired form of fossil fuels. The focus in particular is on the generation of electricity from coal and natural gas with sharply reduced emissions of greenhouse gases, especially CO₂.

• Technologies and geologic settings suitable for the storage of CO₂ produced from electricity generation and other industrial processes.

• Environmental concerns that affect the future of fossil-fuel supply and use.

Given constraints on time and resources, the AEF Committee chose not to address issues relating to the current energy infrastructure, for example, the status of natural gas pipelines, oil refineries, rail and barge transportation for coal, and liquefied natural gas terminals.

Worldwide, the amount of oil, gas, and coal that can ultimately be produced is very large. Estimates of ultimately recoverable resources are uncertain, however, because they include not only those that are discovered though not yet economically or technically recoverable but also those that are yet to be discovered. Nev-