clathrates) represent the bulk of the remain ing energy resources. With anticipated technological improvement, even these currently unconventional sources are likely to become cost-competitive with nonfossil energy sources. Unconventional energy deposits are more evenly distributed among countries than conventional fossil resources are. For example, virtually every nation with a coastline has natural gas in the form of gas hydrates.

Even if conventional oil and gas resources prove to be limited, coal resources are virtually unlimited. Increases in the cost of ener gy will be limited ultimately by the cost of transforming coal into liquids and gases-a cost that is relatively well understood. Fossil fuel energy therefore will be available and may well be cost-competitive for the next century and beyond.

Changing the Energy System

Fundamental shifts in the energy system have occurred very slowly. They have been driven principally by the demand for new energy services and the availability of supply Oil, which has been in use since at least the 1850s, did not surpass coal as the predominant global fuel until the 1960s. Its growth was very slow until transportation demand started to grow rapidly around the middle of the 20th century. Natural gas, which has been used in small amounts since the early 1800s, did not become a significant fuel source until seamless tubing became available in the 1940s, allowing for low-cost, long-range transport. Unlike oil, where the increased usage was driven by the demand for new energy services, the growth of natu