OIL

Oil comes from crude oil, which is a mix of hydrocarbons with some oxygen, nitrogen, and sulfur impurities. One barrel of oil (42 U.S. gallons) can provide about 6 million Btu. Crude oil reserves are found all over the world, but the Middle East alone has about 63 percent of the known reserves. Of the oil consumed in the United States, most is used in transportation, and much of the rest goes to industrial, commercial, and residential uses. Crude oil is used to produce not only a range of fuels, but also petrochemical ingredients for plastics, inks, tires, pharmaceuticals, and a host of other products.

High-tech oil exploration technology and practices have led to the discovery of as many new reserves as have already been used. To make the most of this valuable resource, energy producers are developing more efficient refining methods, product makers are finding more efficient ways to use petrochemicals, and manufacturers are developing more efficient cars. New techniques of locating and extracting oil from the earth are also making it possible to recover oil that was once too expensive to produce.

Oil is usually recovered by drilling wells through the non-porous rock barrier that traps the oil. In general, about 30 percent of the oil trapped can be economically recovered by pumping. «Secondary» recovery can remove another 10 percent, by flooding the well with high-pressure water or gas. Another 10 percent can sometimes be recovered with «tertiary» methods that heat the oil to scrub it out. About half of the oil is left trapped in the rock. Oil producers are continually seeking economical ways to recover more of this oil.

The oil refining process separates crude oil into different hydrocarbons and removes impurities such as sulfur, nitrogen, and heavy metals. The first step is fractional distillation, a process that takes advantage of the fact that different hydrocarbons boil at different temperatures. In a tall tower called a fractionating column, crude oil is heated until it boils. Horizontal trays divide the column at intervals. As the oil boils, it vaporizes. Each hydrocarbon rises to a tray at a temperature just below its own boiling point. There, it cools and turns back into a liquid.

The lightest fractions are liquefied petroleum gases (propane and butane) and the petrochemicals used to make plastics, fabrics, and a wide array of consumer products. Next come gasoline, kerosene, and diesel fuel. Heavier fractions make home heating oil and fuel for ships and factories. Still heavier fractions are made into lubricants and waxes. The remains include asphalt.

The refining process then continues, with heavy fractions converted into lighter fractions. In most cases, «cracking» processes are used to transform large (heavy) hydrocarbon molecules and make the smaller, lighter molecules such as gasoline and jet fuel. Better refining technologies have made it possible to produce over 21 gallons of gasoline from a 42-gallon barrel of crude oil-a remarkable advance over the industry's early days, when a barrel of oil yielded just 11 gallons of gasoline.

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