In Japan and Western Europe, naphtha (or crude gasoline) is by far the most important feedstock available to the chemical industry from the oil refineries. A decreasing availability of natural gas has also led to the increasing use of naphtha in the USA. Olefins such as ethylene, propene, butenes, and butadiene as well as the aromatics benzene, toluene, and xylene can be obtained by cracking naphtha. Of less importance are heavy fuel oil and refinery gas which are employed together with natural gas for the manufacture of synthesis gas. The latter forms the basis for the manufacture of ammonia, methanol, acetic acid, and ‘0x0’ products. The process technology largely determines the content and yield of the individual cuts.