Tesoro Logistics of Texas, working in North Dakota, said there were no injuries associated with the spill. It said no water was contaminated and the surrounding environment should be shielded from any major damage.
"The released crude has been contained, and remediation is in progress," Tesoro said.
Kris Roberts, a geologist with the North Dakota Department of Health, told the Williston (N.D.) Herald the spill was discovered Sept. 29 and had soiled about 7 acres of land. The closest residential home is about a half-mile from the site.
Roberts said Thursday the spill, discovered in late September, was "big, but not a record breaker."
The newspaper said the company had recovered more than 1,000 barrels of oil during its initial response.
"Protection and care of the environment are fundamental to our core values, and we deeply regret any impact to the landowner," Tesoro Chairman and Chief Executive Officer Greg Goff said in a statement.
The company said it expected the cleanup to cost about $4 million.
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