BILLINGS, Montana (Reuters) - Montana Governor Brian Schweitzer continued on Friday to press Exxon Mobil over an oil spill into the Yellowstone River and threatened to take the company to court as clean-up continued a week after the leak.

Schweitzer has been increasingly critical of Exxon in the days since one of its pipelines burst on July 1, spilling what the company estimates was up to 42,000 gallons of oil into the river.

"We're going to hold them liable in court," Schweitzer told reporters following a public meeting in Billings, the Big Sky state's largest city.

Exxon, which said it was committed to a safe, effective clean-up operation, promised to "stay and make this right for the people of Montana," spokesman Pius Rolheiser said in an emailed statement.

Montana formally opened a state office in Billings on Friday to address residents' health and environmental concerns in the aftermath of the spill, a day after Schweitzer withdrew the state from a joint command team over what he said was the company's failure to provide information.

The Democratic governor has sent a letter to Exxon asking the oil giant to spell out the chemical characteristics of crude that flowed through the pipeline, which was buried in the Yellowstone River streambed.

Schweitzer, a trained soil scientist, urged Montana residents to document damage and collect soil and water samples in containers that officials have provided them.

The governor has also warned Exxon not to work on the damaged pipeline without oversight by Montana and federal environmental officers. He has demanded the company preserve all documents related to the rupture and has asked federal regulators for the pipeline's safety records.

Exxon has brought hundreds of high-paying jobs to several Montana communities, including Billings, where oil from the now ruptured Silvertip pipeline was refined.

Schweitzer's apparent frustration with Exxon came to a head amid complaints from Montana residents that calls to Exxon's hotline went unreturned for days.


Exxon has apologized for the spill that dumped toxic substances into a river prized for near pristine waters, wildlife habitat and world-class fisheries.

The company said it shut down pumps on the pipeline to stop the oil flow within six minutes of discovering that something was wrong.

High and turbulent waters have made it difficult for boats to navigate the Yellowstone, hampering clean-up efforts and a probe of what caused the pipeline to rupture just west of Billings.

Schweitzer has pledged the state's new office dealing with the spill would respond to each inquiry within 24 hours.

"This is your office, five days a week, eight hours a day until this mess is cleaned up," he told a gathering of about 150 people, including residents who say oil fumes caused them respiratory distress, fainting and other health problems.

"Montana is responsible for managing that river. There are damages and no one from Exxon has sidled up and offered us a check," Schweitzer said.

Federal officials said shoreline contamination along the Yellowstone -- the longest free-flowing river in the lower 48 states -- has been observed over an area stretching at least 240 miles downstream from the spill site.

Gary Hammond, supervisor of the Montana Fish, Wildlife and Parks regional office in Billings, said scientists believe chemical exposure of river- and wetland-dependent animals and fish may prove devastating for years to come.

"This is a long-term problem," he told Reuters.

In a press conference Friday, National Wildlife Federation's senior scientist Doug Inkley said only 10 to 15 percent of oil spilled is ever recovered.

"Unfortunately, I am a veteran of previous oil spills and I am personally dismayed about what I'm seeing with this oil spill," Inkley said.

(Additional reporting by Molly O'Toole, editing by Alex Dobuzinskis, Cynthia Johnston and Bernard Orr)

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