The indefinite shutdown of a key source of U.S. oil production should draw public attention to the larger and increasingly precarious global petroleum picture.

BP's decision to stop the flow of oil from the Prudhoe Bay oil field, which provides about half of the 800,000 barrels of oil produced daily on Alaska's North Slope, adds a new dimension to the already uncertain international oil-supply situation. BP says it is going to replace 16 miles of pipeline because of corrosion problems to avoid a rupture that could lead to a major oil spill. The company, which operates the Prudhoe Bay fields for itself and other companies, experienced the largest oil spill ever on the North Slope (270,000 gallons) in March.

The loss of production is expected to increase pump prices, especially on the West Coast where most of the Alaskan oil is sent to be refined. But the broader issue is that even before the shut down, oil production on the North Slope had long since peaked and was in decline. The same is true of many oil fields around the world, including those in the North Sea and Mexico.

While the world may be in no danger of running out of oil anytime soon, its ability to provide sufficient production to meet ever- growing demand is being challenged on several fronts. For years, U.S. oil companies were fond of noting that new discoveries exceeded their annual production. While individual companies may in some years manage that feat, globally that's no longer true, and hasn't been since the early 1980s.

Geologists doubt there are many "monster" oil fields left to discover, so that in 2004, while global oil consumption amounted to 30 billion barrels of oil, only 8 billion barrels of new oil reserves were discovered.

In addition, many old oil fields have peaked and are in decline. This includes at least two of the world's three largest oil fields: Mexico's Cantarell field in the Gulf of Mexico, the second-largest oil field, which is in rapid decline, and Kuwait's Burgan field. The largest oil field, Saudi Arabia's Ghawar, may also be in decline.

And it gets worse. According to Kjell Aleklett, a professor in physics at Sweden's Uppsala University and the president of the Association for the Study of Peak Oil & Gas, 54 of the 65 largest oil-producing countries have passed the peak of production. U.S. oil production peaked in 1970-71, with production on Alaska's North Slope peaking at 2 million barrels per day in 1988, which helps account for our growing dependence on imported petroleum.

The other side of the coin is the rising global consumption of oil. Many energy experts are concerned about the world's ability to meet the rising demand for oil, which is growing especially fast in China and India. Current global consumption of 85 million barrels per day of oil is projected by the International Energy Agency to grow by about 50 percent by 2030. While there are new oil fields coming on line over the next few years, they will do well to cover the declines in old fields and possibly provide some modest increase above current global production. Major increases in Saudi oil production are often cited as meeting growing world demand, but while some increase is projected, the Saudis themselves don't believe it will be anywhere near what others seem to expect.

As with many major issues the world faces today, meeting future energy needs is a matter fraught with conflicting views and statistical projections that confuse rather than enlighten. The optimistic view that technological advances and new discoveries will more than meet our energy needs for the coming decades is the prevailing and operative view. But the pessimists, many of them with long associations with the oil industry, are warning that recent spikes in oil prices are only the beginning.

But straight lines occur neither in nature or in markets. If oil prices get too high, they will likely trigger a worldwide recession, which will cut demand and lower oil prices in time. But the true bottom line is this: However much oil is left in the ground, it is a finite resource and the more difficult it is to find and refine into a usable product the more expensive it becomes.

If we were acting with prudence, we would seek to extend our supply of oil through intense efforts at conservation, efficiency and development of alternative technologies and energy sources.

In not doing that, the nation and the world are playing fast and loose with perhaps the Earth's greatest material endowment, which has singularly made the modern would possible. We would do well to ponder what the world will be like when the Age of Oil has run its course.