The Trans Alaska Pipeline System (TAPS) was being restarted on Tuesday after a shutdown of about six hours caused by a leak, operator Alyeska Pipeline Service.
The system will be back to its normal flow rate of 800,000-barrels-per-day by late Tuesday night, Alyeska spokesman Mike Heatwole said.
The pipeline system, which TAPS operates for oil companies, was shut on Tuesday after an oil spill was detected nearly 200 miles south of the big Prudhoe Bay field on Alaska's North Slope. The pipeline system carries about 15% of U.S. crude oil production.
In 2006, its average daily flow was about 760,000 bpd, or 5% of the 15.2 million barrels run through U.S. refineries every day.
On Tuesday, up to 500 gallons (1,893 liters) of crude spilled before the line was shut down, environmental regulators said. The spill, equal to about 12 barrels, has since been contained and is being cleaned up.
The short shutdown did not affect oil shipments from the pipeline's marine terminal in Valdez, Heatwole said. Alyeska is still investigating what went wrong, he said. "What we really want to find out is why (a threaded fitting) was loose in the first place," he said.
Earlier, the on-scene coordinator for the Alaska Department of Environmental Conservation, Ed Meggert, said the cause of the leak was likely a faulty weld. The spill was confined to a gravel pad and has affected an area no more than 25 feet across, Meggert said. "In terms of cleanup, it really shouldn't be too difficult," he said.
Heatwole said the spill was discovered by a worker doing a routine maintenance check and the pipeline was shut down within minutes, at 8:35 a.m. local time, he said.
BP, Exxon Mobil and ConocoPhillips are the main owners of the system. A unit of Chevron and Koch Alaska Pipeline own minor shares.