The warnings keep piling up. Author Paul Roberts cautions his readers about "The End of Oil." National Geographic's cover story last month examined how the world might survive "After Oil." The Economist magazine asks, "Is the age of oil drawing to a close?"
With the discomfort growing, consumers are considering fuel-efficient cars. Industry has gotten serious in its search for alternatives. New efforts are focused on wind, solar, nuclear, and even old, reliable coal (in a cleaner version) for the energy future.
But is the world really running out of oil? The short answer is no. Earth is swimming in the stuff. What's changed is that the era of cheap oil - a period that has lasted 150 years - is showing its age. Only a dramatic breakthrough - either in technology or consumption patterns - can forestall its conclusion in a decade or two.
If it happens, the end of cheap oil would have a profound effect: stunting world economic growth, constraining China's rise, and challenging Western lifestyles. America's joy ride, in particular, could come to a screeching halt.
"The US has 2 percent of the world's proven oil reserves. But it burns 25 percent of the world's transportation fuels," says an analyst close to the oil industry who asked not to be named. "This isn't going to work out in the long run."
The problem isn't readily apparent from a supply viewpoint. When the world's first oil well was sunk in Pennsylvania in 1859, the Earth contained at least 6 trillion barrels of crude oil, geologists estimate. So far, we have used only about 1 trillion barrels.
So what's all the fuss about?
Part of the worry has to do with access. Of the original 6 trillion to 8 trillion barrels in the ground, the industry is capable of extracting only about half - 3 trillion to 4 trillion barrels. Lots of oil is locked in difficult underground formations that are hard, if not impossible, to exploit using current technology.
Moreover, those first 1 trillion barrels were among the easiest to reach. The days of easy gushers and overnight millionaires are long gone. Now the going gets harder.
Where underground formations are highly favorable, as in the Gulf of Mexico and Saudi Arabia, oil drillers can often retrieve 60 percent of the oil. But in marginal formations such as some found in Oklahoma, the average rate of recovery can be as low as 8 to 10 percent. Worldwide, the average is about 35 to 40 percent, according to the US Energy Information Administration.
In short, only 2 trillion to 3 trillion barrels may remain for our use.
Even more worrisome is the demand equation. It took 146 years for the world to use the first 1 trillion barrels. The next 1 trillion barrels will be gone by around 2030. After that, we could have as little as 1 trillion or 2 trillion barrels of conventional oil left.
Some experts who follow these issues closely are getting worried. One big change, particularly in the past two years, has been increasing international competition for oil supplies.
During most of the past century, it was mainly the United States, Japan, and Europe that vied for the world's petroleum supplies. Now other nations like China and India are developing their own needs for oil to fuel their factories and their rapidly expanding fleets of automobiles, trucks, and airplanes. That could set off a scramble for worldwide oil reserves, and it seems to assure that higher prices - at least higher than we are accustomed to - are here to stay.
While the nations with the largest reserves, mostly in the Middle East, have periodically offered to increase production, there is also concern that they've showed few signs of boosting their overall capacity to pump oil.
Still, the long-term outlook is murky. Even industry leaders don't always see eye to eye.
There's no impending worldwide supply crisis, according to Rex Tillerson, president of ExxonMobil, the world's largest petroleum company. Oil and natural gas "are likely to remain the primary energy source through the middle of the century," he said in a speech this year.
A recent ExxonMobil study of world energy resources supports that view. It found that oil should remain plentiful and affordable at least through 2030, which was the time limit of the report. Rising worldwide demand will be met primarily by increased production in the Middle East, the study concludes.
We already face "a new energy equation," counters David O'Reilly, chairman and CEO of ChevronTexaco. Three factors are squeezing oil supplies - globalization, economic growth, and falling oil output in several nations, including the US.
"Oil is no longer in plentiful supply," Mr. O'Reilly said in a speech this year. "The time when we could count on cheap oil and even cheaper natural gas is clearly ending."
When it finally comes, the end of cheap petroleum would be felt nowhere more keenly than in America, a nation built on low-cost, plentiful energy, and cheap oil in particular. Long, leisurely Sunday drives and Saturday night cruising down Main Street in hot rods with 25-cent-a-gallon gasoline were traditions fused into the American psyche in the era after World War II. Today's suburban American lifestyle - built around long commutes to work and large, energy-hungry houses - assumes that low-cost fuel will be available indefinitely.
For years, American prosperity was fueled with oil because the country had so much of it. The country mostly produced as much as it used, but when more was needed, plenty of imports were available from Venezuela, Canada, and other friendly nations.
Today, the US position is more precarious. US output of crude oil and natural-gas liquids (like propane) hit a peak in 1970 of 11.3 million barrels per day. Then the slide began. By 2004, US production had slumped to just 7.2 million b.p.d., even though US consumption had climbed to more than 20 million b.p.d.
Nor is domestic production likely to spike upward because of some new find, analysts say. By one estimate, some 80 percent of all the wells ever drilled in the world have been drilled in the US.
Because of all this, the US is now highly - perhaps even dangerously - dependent on other nations for its transportation fuels, particularly Canada and Mexico, but also Saudi Arabia, Venezuela, Nigeria, and Iraq.
One immediate problem for the US is that its leaders in Washington too often see the oil supply situation "largely as a political problem," argues Mr. Roberts, author of "The End of Oil" in 2004. Too many of them insist that if only the US government would allow oil drilling in the Arctic National Wildlife Refuge, or if only US companies were allowed back into the rich Saudi oil fields, the problem would be solved, he adds.
Yet rising prices for gasoline and crude oil already demonstrate something else - that worldwide demand is gaining on, and could soon overtake, supply, Roberts says. If demand keeps rising, he adds, "I don't think anyone in the West knows" whether oil exporters, particularly in the volatile Middle East, can - or will - meet that demand.
• First of three articles. Wednesday: Why gasoline prices are high.