By Ben Berkowitz
NEW YORK (Reuters) - A pipeline operated by Exxon Mobil Corp leaked as many as 1,000 barrels of crude oil into the Yellowstone River in Montana and has been shut down, the company said.
Exxon officials said on Sunday there were traces of oil up to 10 miles downriver from the site of what they called a "very unusual" event.
The oil company said it had slowed processing rates at its Billings refinery following the leak but did not expect supply disruptions in the area.
Exxon found the leak from the EMPCo pipeline early on Saturday morning. The pipeline runs only in Montana, from Silver Tip to Billings.
The cause of the leak remains unclear. Exxon estimated the oil release at anywhere from 750 to 1,000 barrels. One barrel of oil is equivalent to 42 gallons (163 liters), and the pipeline typically transports 40,000 barrels a day.
"We had no indications that there were any issues with this pipeline," Gary Pruessing, the president of EMPCo, told reporters on a conference call on Sunday.
Pruessing said the pipeline had been shut in May as a precaution as the river approached a high-water point, but that it was judged to be safe and turned back on.
The Billings Gazette on Sunday cited conflicting reports from Exxon officials as to the extent of the leak. The paper carried pictures of absorbent bags piled along the side of a road running parallel to the river, ribbons of oil sticking to logs and one of a turtle stuck in oily mud.
Environmental cleanup firm Clean Harbors is on-site assisting with the early remediation efforts, Exxon said.
The leak came one day after a Maryland jury awarded plaintiffs suing Exxon $1.5 billion in damages for a 2006 leak at a gasoline station.
Exxon said a claims hotline it set up for the Montana spill had already received 41 calls.
(Editing by Dale Hudson and Maureen Bavdek)