An oil response team from the Billings refinery deployed booms in a channel feeding the Yellowstone River. Rachel Moore, a spokeswoman for Exxon, told Bloomberg News in an e-mail statement that the Texas oil company likely wasn't responsible for the spill.
"Exxon Mobil has no pipelines or similar oil containing equipment in close proximity to the leak," she was quoted as saying.
Around 1,200 barrels of oil spilled from Exxon Mobil's Silvertip pipeline into the Yellowstone River near Billings, Mont., in early July.
Last month, the U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration said it approved of the energy company's return-to-service plan, which allows Exxon to restart operations on Silvertip.
Exxon faces a class-action suit for its response to the July spill.
The PHMSA added it was still determining whether Exxon broke safety regulations during the days leading up to the July 1 failure on the pipeline.