With demand high, supplies squeezed, prices climbing and refineries already running flat out, what if something really went wrong? Something like a terror attack on crucial oil installations in Saudi Arabia or in the United States, or something less sinister but just as disruptive, like a fire or accident at a major refinery or port or a flare-up of civil or labor turmoil in Nigeria or Venezuela?
Industry experts say that the drum-tight American fuel market has become unusually vulnerable to any such nasty surprises, because there is little spare capacity available and because traders, executives and policy makers are nervous about terrorism and other threats - to the point that crude oil now carries a "risk premium" of 12 to 25 percent, analysts estimate.
"The problem is, we've already tasted some of these events in one form or another," said Daniel Yergin, chairman of Cambridge Energy Research Associates, an energy analysis company. "The threat of an oil shock is very tangible. If an oil trader wants to think about risk, all he has to do is turn on the television."
Just how big a risk premium traders will demand on oil is a subjective calculation, driven up or down from day to day by news developments. One energy strategist, Fadel Gheit of Oppenheimer & Company in New York, estimated that worries about Nigeria contributed about $1 a barrel; Venezuela another $3; the situation in Iraq, $4 more; and jitters about new trouble in Saudi Arabia, $5 a barrel. "In a psychologically charged market, bad news travels faster than good news," Mr. Gheit said.
Without the black cloud of vulnerability from the market, many analysts say, crude might trade for $30 or $35 today instead of nearly $40.
Gasoline prices, in turn, reflect worries about crude oil volatility overlaid with jitters about refineries and low inventories.
To be sure, there are important differences between conditions today and 30 years ago, when tensions in the Middle East disrupted oil supplies. Few economists see much danger of the rationing, gas lines, sharp inflation and deep recession of those years recurring today. Energy is a smaller component of the overall economy now, prices are still fairly low in inflation-adjusted terms, and measures taken after the oil shocks of the 1970's provide some protection, most notably the creation of the Strategic Petroleum Reserve, with a capacity of 700 million barrels.
Even so, President Bush's decision to fill the reserve after the terror attacks of September 2001 has been one of the factors driving up oil prices in recent months, along with reports that China, which recently surpassed Japan as the second-largest importer of oil, is going ahead with plans to build its own petroleum reserve. The Bush administration has resisted calls to release oil from the American reserve.
The reserve now holds about 660 million barrels, making it the world's largest source of stockpiled petroleum. Other domestic stocks, held commercially in refineries, pipelines or storage tanks, stand at about 299 million barrels, about 5 percent below the average level of the last five years, according to the Energy Information Administration.
Analysts say another immediate issue is the ability to turn the available oil into fuels. Consolidation over the last two decades has cut the number of refineries in the United States in half, to 153 from 301, and the survivors are working at well more than 90 percent of maximum capacity.
Even a small disruption, like a fire or maintenance mishap, could quickly result in a temporary price spike. For example, when a relatively small 85,000-barrel-a-day refinery operated by Valero Energy in Krotz Springs, La., shut for less than a day earlier this month because of a power failure, gasoline futures prices shot up by 5 cents a gallon.
No relief is in sight. "We haven't built a new refinery in this country for three decades," Lee Raymond, the chairman of Exxon Mobil, the nation's largest energy company, told reporters this week after the company's annual meeting. "Refineries historically haven't made money, and I don't see a lessening of environment restrictions."
As a result, the United States now imports about 10 percent of its refined gasoline, mainly from Europe and South America. But many foreign refineries have struggled to adapt as many states have switched to requiring cleaner-burning blends of gasoline this year.
Political tensions in Venezuela, historically a leading supplier of both crude oil and gasoline to the United States, have made matters worse. Opposition to President Hugo Chávez within the state oil company, Petróleos de Venezuela, resulted in a management purge that hobbled the company, to the point that the country has recently had to import gasoline.
Analysts estimate that Venezuela is now producing only 2.5 million barrels of oil a day, down from more than 3 million before the political crisis; much of the missing production would have been destined for the American market.
Newer to the picture are the growing concerns about sabotage and unrest spilling over from Iraq to other nations in the gulf. "The real fear factor is at the heart, within Saudi Arabia," said Fareed Mohamedi, chief economist at PFC Energy, a consulting firm in Washington. "The idea that terrorists could target specific facilities within the kingdom brings the fear to a new level."
Attacks in early May that killed five Western contractors in Yanbu, a Saudi refinery and petrochemical center on the Red Sea coast, did not disrupt oil supplies directly, but they created anxiety about the security of other facilities, not least because Saudi officials have suggested that the attacks may have been the work of a regrouping Qaeda terror network that intends to strike again.
"That's why all the Saudi talk about increasing output has already been discounted without having a downward effect on prices," Mr. Gheit of Oppenheimer said. "It's a psychologically charged market that's trading on the fear that the O.K. Corral atmosphere of Iraq could spread to Saudi Arabia."
A year ago, analysts say, the world could manage without Iraq's two million barrels or so of daily production, but recovery in much of the developed world and roaring growth in China and India mean that the global market now needs every drop.
In fact, global oil demand is expected to grow faster this year than at any time since 1988, rising by about 2 million barrels, to 80.6 million barrels a day, according to the International Energy Agency. So the production gains from the painstaking reconstruction of Iraq's oil infrastructure in the last year have already been absorbed by export markets. A failed attack in April on an important Iraqi offshore terminal was a reminder of how tenuous those gains might prove to be.
Along with security concerns abroad, the fear of attacks on energy hubs within the United States also haunts the market. While there is little public evidence that such attacks are being planned, the F.B.I. issued a warning in March that Al Qaeda might be preparing to blow up pipelines and refineries in Texas ahead of the November elections.
The Houston area, with two of the four largest oil refineries in the United States and much of the infrastructure used to transport oil and natural gas around the country, has been mentioned as the most sensitive potential target. The city is also the intellectual and financial center for the global energy industry.
"A possible attack is absolutely a concern for us," said Rick Hagar, spokesman for the East Harris County Manufacturers Association, which represents 125 industrial concerns along the Houston Ship Channel, among them refineries, shipping companies and petrochemical plants. "It's something to worry about night and day."