What is Oil?

According to the most widely accepted theory, oil is composed of compressed hydrocarbons, and was formed millions of years ago in a process that began when aquatic plant and animal remains were covered by layers of sediment. Over millions of years of extreme pressure and high temperatures, these particles became the mix of liquid hydrocarbons that we know as oil.  Different mixes of plant and animal remains, as well as pressure, heat, and time, have caused hydrocarbons to appear today in a variety of forms: crude oil, a liquid; natural gas, a gas; and coal, a solid. Even diamonds are a form of hydrocarbons.

The word "petroleum" comes from the Latin words petra, or rock, and oleum, oil. Oil is found in reservoirs in sedimentary rock. Tiny pores in the rock allowed the petroleum to seep in. These "reservoir rocks" hold the oil like a sponge, confined by other, non-porous layers that form a "trap."    

The world consists of many regions with different geological features formed as the Earth's crust shifted.  Some of these regions have more and larger petroleum traps.  In some reservoir rock, the oil is more concentrated in pools, making it easier to extract, while in other reservoirs it is diffused throughout the rock.

The Middle East is a region that exhibits both favorable characteristics -- the petroleum traps are large and numerous, and the reservoir rock holds the oil in substantial pools.  This region’s dominance in world oil supply is the clear result. Other regions, however, also have large oil deposits, even if the oil is more difficult to identify and more expensive to produce.  The United States, with its rich oil history, is such a region.

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