Petroleum is a naturally occurring, smelly, yellow-to-black liquid consisting of  complex mixture of Hydrocarbons of various molecular weights that are found in Geologic Formations beneath the Earth's surface.  It is a Fossil Fuel that is formed when large quantities of dead organisms, usually are buried underneath Sedimentary Rock and undergo intense heat and pressure.

Petroleum is also used in manufacturing a wide variety of materials. Petroleum includes crude oil and many other liquid and gaseous components. Different components of petroleum are separated out through fractional distillation as their boiling points vary. The fractional distillation is done in the refineries. High grade petroleum is used in air planes, cars and diesel is used in diesel engines. Perfumes, shoe polish, wax etc are made using petroleum products. Even the tar that is used on the road surfaces is obtained from petroleum and is actually the crudest form that remains as sediment after other useful products are distilled.

diagram