WASHINGTON - Osama bin Laden's personal files revealed a brazen idea to hijack oil tankers and blow them up at sea last summer, creating explosions he hoped would rattle the world's economy and send oil prices skyrocketing, the U.S. said yesterday.

The newly disclosed plot showed that while bin Laden was always scheming for the next big strike that would kill thousands of Americans, he also believed a relatively simpler attack on the oil industry could create a worldwide panic that would hurt Westerners every time they gassed up their cars.

U.S. officials said the tanker idea, included in documents found in the compound where bin Laden was killed nearly three weeks ago, was little more than an al Qaeda fantasy. But the FBI and Department of Homeland Security issued a confidential warning to police and the energy industry yesterday. The alert, obtained by the Associated Press, said that al Qaeda had sought information on the size and construction of oil tankers, had decided that spring and summer provided the best weather to approach the ships, had determined that blowing them up would be easiest from the inside and believed an explosion would create an "extreme economic crisis."

"We are not aware of indications of any specific or imminent terrorist attack plotting against the oil and natural-gas sector overseas or in the United States," Homeland Security spokesman Matthew Chandler said in a statement yesterday. "However, in 2010 there was continuing interest by members of al Qaeda in targeting oil tankers and commercial oil infrastructure at sea."

With about half the world's oil supply moving on the water, industry and security experts have warned for years that such an attack would be a jolt to global markets. That's particularly true if terrorists carried it out in one of the narrow waterways that serve as shipping chokepoints.

"You start blowing up oil tankers at sea and you're going to start closing down shipping lanes," said Don Borelli, senior vice president of the Sufan Group security firm and a former FBI counterterrorism agent. "It's going to cause this huge ripple through the economy."

Still, even if al Qaeda were able to blow up one of the supertankers that move oil around the globe, it would barely dent the world's oil supply, said Jim Ritterbusch, president of Ritterbusch and Associates, who has been trading oil contracts since the futures market opened on the Nymex in 1983. A tanker holds about 2 million barrels, or enough to supply world demand for about a half hour.

The terrorist threat to oil infrastructure is nothing new. Members of a British terror cell that hoped to hijack trans-Atlantic airplanes in 2006 had also made plans to attack oil and gas targets in Britain. Al Qaeda's franchise in Yemen has attacked pipelines.

Yesterday's alert was significant mostly because it linked the scheme directly to bin Laden, meaning the idea probably has circulated among al Qaeda's most senior leaders.