The petrochemical industry was incepted around 70 years ago with the production of isopropyl alcohol from propylene. The word Petrochemical describes the chemicals obtained from Petroleum Hydrocarbons and Natural gas directly or indirectly. The production of Petrochemicals is one of the dominant industries of the developed countries and a driving force and future goal for developing countries. With the advent of catalytic reforming, aromatic hydrocarbons have become available in large quantities from a stable source, namely crude oil and natural gas. The aim of this dictionary is to facilitate communication between those contributing, directly or indirectly, to the development of petrochemicals: students, engineers, equipment manufacturers, oil companies and last but not the least producing and consuming countries. The approach is descriptive. The editor has examined numerous reliable scientific and technical documents and provides the reader with the actual terms and expressions he has found. This dictionary includes 4500+ terms.