Most of the oil that spilled from a Canadian-owned pipeline into a southern Michigan river has been contained and between 5,000 and 6,000 barrels of oil have been recovered, Enbridge officials say.

Oil sheen is shown Thursday in the Kalamazoo River in Battle Creek, Mich. (Paul Sancya/Associated Press)

"It appears that the oil is now contained, and we are transitioning to our cleanup plan," the Calgary-based company said Friday.

The company said 26 containment booms have been placed along the Tallmudge Creek and the Kalamazoo River to stop the advance of the oil, which is being pumped into tankers.

The company said about 19,500 barrels of oil — roughly 3.1 million litres — leaked from the pipeline, but the U.S. Environmental Protection Agency said the amount could be as high as 3.8 million litres.

'We'll know more once we're able to capture, collect and haul away the oil," Enbridge spokesman Alan Roth told CBC News.

Michigan Gov. Jennifer Granholm, who took a helicopter tour over the spill site Friday, said there had been "significant progress" in the containment and cleanup. She said she did not see any oil sheen on Morrow Lake.

Environmental Protection Agency administrator Lisa Jackson said she is "very confident" the spill won't reach Lake Michigan. Granholm had warned of a "tragedy" if the oil were to reach Lake Michigan.

While much of the oil has been contained, Ralph Dollhopf, the federal co-ordinator for the EPA on the scene, said cleaning up the river and surrounding areas could take months.

But Roth said Enbridge is "prepared to stay until the local community and the people in the area agree the cleanup is done to their satisfaction."

Hundreds of workers and contractors were working on the oil spill Friday, along with 36 boats, 12 tanker trucks and more than 70 vacuum trucks, the company said.

Enbridge detected the spill — which sent oil flowing into a creek that feeds the Kalamazoo River — early this week.

Enbridge facing questions

As the cleanup continues, the company is facing questions about how the spill happened.

An Enbridge containment boom is set downstream from Battle Creek, Mich. (CBC)

Crews are trying to dig down to the damaged section of pipe so investigators can determine what went wrong.

Getting to the pipe has been difficult, because it is located in a marshy area, but Enbridge officials said they expected to uncover the damaged section of pipe Friday.

The Associated Press reported that the company has a history of pipeline problems, including leaks and regulatory violations.

Enbridge Inc. and its affiliates have been cited for 30 enforcement actions since 2002 by the Pipeline and Hazardous Materials Safety Administration, which is the U.S. Department of Transportation's regulatory arm, the news agency said.

In a warning letter sent Jan. 21, the regulator told the company it may have violated safety codes by improperly monitoring corrosion in the pipeline responsible for the spill.

Steve Wuori, an Enbridge executive vice-president, said the company was doing maintenance all along the pipeline this year, but the section at the leak site was not scheduled for replacement.

With files from The Associated Press