Around 1,200 barrels of oil spilled from Exxon Mobil's Silvertip pipeline into the Yellowstone River near Billings, Mont., in early July. Flooding slowed cleanup efforts and teams were sent in to remove debris soaked with oil after water levels dropped.
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.
"PHMSA has performed an extensive review of information and monitored the repairs made by Exxon Mobil to ensure the full line's ability to resume service in a safe and environmentally sound manner," the regulator said in a statement.
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.
Silvertip had carried oil from tar sands projects in Canada since the 1980s but that type of oil wasn't at the site of July spill.