Exxon in October said it expected to pay more than $100 million in cleanup operations for the July 2011 rupture near Billings, Mont. An estimated 1,200 barrels of oil spilled from the Silvertip pipeline into the Yellowstone River in the incident.
A report from the Pipeline and Hazardous Materials Safety Agency said the severity of the spill could've been diminished had Exxon's emergency procedures required automatic shut-off valves, Montana broadcaster KULR-8 News reports.
Exxon officials told the broadcaster, however, that it would be "inappropriate to comment on the details of the report until the company has received sufficient time to review and analyze its findings."
Scouring of the pipeline, which was about 4 feet below the river bottom, is suspected of contributing to the rupture of Silvertip.
The PHMSA report stated that Exxon likely was unaware of riverbed conditions as the Yellowstone River hadn't experience major flooding since the pipeline was built in 1991.
After the spill, Montana Gov. Brian Schweitzer called for a review of the 9,000 pipelines that cross waterways in the state.