Stephen Krause Jr., age 16, of Providence, R.I., for his question:

WHAT ARE SYNTHETIC FUELS?

Synthetic fuels are oil or gas produced from coals, shale formations and tar sands as a substitute for petroleum and natural gas. Made from natural raw materials, synthetic fuels are actually natural fuels that require costly processing.

Four methods are used to convert coal to gas or oil: synthesis, carbonization, extraction and hydrogenation.

Synthesis, which was developed in the 1870s to produce gas, requires that coal be pulverized and mixed with oxygen and steam at high temperatures. It is then purified.

Carbonization is the heating of coal in the absence of air.

Extraction is the dissolving of coal with an organic liquid, then exposing it to hydrogen.

Hydrogenation is the reacting of coal with hydrogen at high pressures, usually in the presence of a catalyst.