PETROLEUM IN ITS STRICTEST SENSE INCLUDES ONLY CRUDE OIL, BUT IN COMMON USAGE IT INCLUDES ALL LIQUID, GASEOUS, AND SOLID HYDROCARBONS.
Petroleum is a mixture of a very large number of different hydrocarbons; the most commonly found molecules are alkanes (paraffins), cycloalkanes (naphthenes), aromatic hydrocarbons, or more complicated chemicals like asphaltenes. Each petroleum variety has a unique mix of molecules, which define its physical and chemical properties, like color and viscosity.
In the international petroleum industry, crude oil products are traded on various oil bourses based on established chemical profiles, delivery locations, and financial terms. The chemical profiles, or crude oil assays, specify important properties such as the oil's API gravity. The delivery locations are usually sea ports close to the oil fields from which the crude was obtained (and new fields are constantly being explored), and the pricing is usually quoted based on F.O.B.