The Trans-Alaska Pipeline System, which carries about 15 percent of U.S. crude oil output, was shut after a leak, forcing oil companies including BP PLC to suspend 95 percent of production from the North Slope. The system, an 800-mile network crossing the northernmost U.S. state, was closed at about 8:50 a.m. Alaska time Sunday, operator Alyeska Pipeline Service Co. said. The leak was probably from an underground section of piping encased in concrete at Pump Station 1, Alyeska said. The shutdown is a further setback for BP, whose well blowout in the Gulf of Mexico in April led to the biggest offshore oil spill in U.S. history. Crude prices rose 21 percent in the second half of last year and reached a 27-month high of $92.58 on Jan. 3 on speculation the U.S. economic recovery will boost fuel demand in the world's biggest oil-consuming country.

New York crude, which traded at $88.03 a barrel on Jan. 7, may climb further if the pipeline problem isn't fixed, said Gavin Wendt, founding director at MineLife Pty Ltd. in Sydney.

"If there's no resolution by tomorrow, we may see prices heading towards $90 a barrel or higher," Wendt said. "The market is very susceptible to supply-side problems."

The pipeline system transported an average 642,261 barrels a day last month, according to Alyeska's Web site. The network starts in Prudhoe Bay on the North Slope and runs to Valdez, the northernmost ice-free port in North America. Since it began operating in 1977, Alyeska has shipped more than 16 billion barrels of oil, according to the Web site.

"Engineers are assessing the situation and developing a plan to safely restart the pipeline," Alyeska said. There were no injuries and no "apparent impacts to the environment," it said, without stating when flow would resume. Federal and state staff are helping with the response and crews began recovering oil about seven hours after the shutdown, Alyeska said.