The petroleum plunge.

Three of America's biggest oil companies are about to take a deep-sea plunge. A record 981 meters (3,220 feet) below the Gulf of Mexico's crashing waves, they plan to begin drilling for oil. Far above, on an anchored offshore oil platform known as Ram-Powell, workers are expected to recover a huge portion of the 15 billion barrels of oil trapped beneath the ocean floor.

Why do we need so much oil? Every time you ride in a car, fly to Grandma's, lace up your gym shoes, wash with soap, or drink from a plastic cup, you're using oil or an oil-based product. Americans collectively soak up 30,274 liters (8,000 gallons) of oil per second, according to British Petroleum, a company that, keeps track of world energy use.

And we've used up most of the oil we can easily retrieve from wells beneath dry land in the U.S. says Jim MacKenzie, an energy scientist at the World Resources Institute. "U.S. oil production peaked in 1970 and has been declining ever since," he says.

Using deep-water platforms like Ram-Powell, adds Jimmy Fox, spokesman for Shell Oil, "is really the last great opportunity for huge, significant oil finds in the U.S." And the more oil we can find in the U.S. - and beneath its surrounding seas - the less we need to import from other countries, like those in the sometimes politically unstable Middle East.

EARTHLY ENERGY

Why is oil so hard to come by? Geologists (scientists who study Earth and its changes) explain that, like coal and natural gas, oil is a fossil fuel. It forms from decayed plants and animals over millions of years. In the Gulf of Mexico, explains Texas A & M geologist Robert Berg, the process begins when dead plants and animals that once lived in the sea or were carried there by rivers settle to the seafloor and pile up. Sediments, like sand, clay, silt, and pebbles that settle out of the water, bury the decaying organisms.

Over time, debris piling up above presses the buried "fossils" down to depths of thousands of feet. At such great depths, pressure from the water and layers above compresses the sediment and organic matter into layers of sedimentary rock, the source for oil.

The pressure and increasing temperatures also cause chemical reactions in the decayed matter, says Berg. These reactions rearrange the matter's hydrogen and carbon atoms to form hydrocarbons, the molecules that make up oil.

How do companies find oil buried so deep beneath Earth's land surface - or beneath the ocean? The black ooze sometimes helps reveal its presence. It naturally tries to flow upward, from high-pressure areas beneath the sedimentary layers to low-pressure areas above. Sometimes, it even escapes through the billions of tiny holes in porous sedimentary rock and bubbles to Earth's surface, geologists But very often, nonporous rocks form traps that block the upward path (see diagram, p. 18).

OIL TOIL

To search for these underground oil reserves, geologists go high-tech. Even when searching for oil beneath the ocean floor, they start far above the sea's surface, with satellites in space. The satellites locate basins, giant "potholes" on Earth, where sediments - and oil - are likely to collect, says geologist Berg. instance, on a satellite map, the Gulf of Mexico appears as a basin into which sediments the Mississippi River have flowed for millions of years.

Next, oil companies map out the types and formations of underground rock. To "see" the rock layers miles beneath the Gulf, geologists often use sonar, a technique that uses sound waves, to conduct seismic surveys. A ship tows a machine that sends bursts of sound down into the water. The different rock layers at various ocean depths reflect at sounds at different time intervals, bouncing "echoes" back to the ship. Scientists on board measure how long it takes each echo to return; the greater the intervals, the greater the depth. Since sedimentary and nonporous rocks reflect sound at different rates, the data indicate where various rock types - and oil traps - lie.

DRILL TEAM

"Nowadays, we use 3-D seismic [surveys] because you just don't drill a well on a hunch," says Shell Oil's Fox. "You have to have very sound science before you commit to spending millions of dollars drilling an exploratory well."

With 3-D maps of underground rock layers, oil companies can zero in on an oil trap in the Gulf, anchor platforms like Ram-Powell, and determine the right spot to drill. Ram-Powell workers will actually drill several wells to make sure they hit pay dirt. If they're on target, oil under high pressure beneath the trap will naturally surge upward through the well's pipes, toward lower pressure above. Pipes will carry the oil to tankers and on-shore refineries, where it will be purified for all its various uses.

Of course, drilling in the wide-open sea with smashing waves and whipping winds can be dangerous - and costly. Ram-Powell, for instance, will cost an estimated $1 billion. And its oil supply will eventually run dry. In fact, the world's oil production might peak somewhere between the year 2000 and 2010, says energy scientist MacKenzie. What's left could run out in as little as 40 years!

Are there any alternatives to ease our dependence on oil? Read the debate at right. Then decide.

OIL OR ALTERNATIVES?

Many people feel that oil is not all its pumped up to be. They say we should be devoting more research and money to finding alternative energy sources rather than drilling for more oil. What do you think? Consider these points:

* Oil pollutes: Tankers and pipelines sometimes leak; refineries, where oil is purified, produce toxic wastes; burning oil pollutes the air.

* Oil is nonrenewable. Once we burn it, it's gone, And we're using it faster than Earth can produce it.

* Energy alternatives (e.g., solar and wind power) don't pollute and will never run out.

* Alternative energies can be costly and unpredictable. for instance, wind power works only in places with steady, strong winds.

* Oil is readily available (for now), and relatively cheap and efficient, industry officials say.

* The U.S. oil industry employs some 1.5 million workers