Alaska ? The trans-Alaska oil pipeline was taken off-line Tuesday after a spill of up to 500 gallons, the pipeline’s operator said.

The crude oil spilled from an aboveground section of the pipeline at a remote gate in the Brooks Range in northern Alaska. The cause of the spill was a failed weld on a threaded O-ring fitting on a bypass line, the state Department of Environmental Conservation said.

Alyeska Pipeline Co., the pipeline’s operator, closed valves on the line, effectively shutting down the pipeline. However, there still was a small amount of oil leaking.

The company was assessing when the pipeline could be restarted, spokesman Mike Heatwole said in Anchorage.

The pipeline was carrying more than 800,000 barrels of oil when it was shut down, Heatwole said. He added that there was plenty of oil stockpiled at the marine terminal in Valdez and that tankers could continue to be loaded with oil for days with no disruption in supply.