What Is Petroleum ( Crude Oil ) ?

Petroleum (petroleum, from Greek πετρέλαιον, lit. "rock oil") or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.

The term "petroleum" was first used in the treatise De Natura Fossilium, published in 1546 by the German mineralogist Georg Bauer, also known as Georgius Agricola.

Petroleum has probably been formed by a slow decomposition of organic matter under the earth's surface. It is found in cavities and crevices, and through the substance of the rock. In mining for it a well 3 or 4 inches in diameter, and sometimes 700 or 800 feet deep, is bored by drills, generally by steam-power. When rock containing petroleum is being bored through, what is called "a show of oil" is found. The chips and water drawn up from the well show and smell of the oil, but, unless the drill strikes a cavity or crevice filled with oil, the well isn't productive. This uncertainty is the most unfortunate peculiarity of oilmining, and makes it, to a great extent, a lottery, for there are no surface indications by which these cavities can be discovered.

Petroleum is much lighter than water, of a dark green or black color, with a peculiar and, to most persons, unpleasant odor. It is commercially divided into two kinds, the heavy, or lubricating oil, and the light oil. The former is more dense, and sometimes of the consistence of thin molasses. It is used, without preparation, for lubricating machinery, for which it is admirably suited. The light oil, before it can be used, is submitted to several purifying processes, the most important of which is distillation.

Petroleum is found in many localities on this continent. Among these may be mentioned as the most important, Canada West, Pennsylvania, Ohio, Western Virginia, California, Kentucky, and Tennessee. The first four yield more than nine-tenths of all now obtained, but it is probable that other regions will yield equally well when as thoroughly explored.