Exxon Mobil contractors put absorbent sheets over oil that came into the backyard of a home along the Yellowstone River near Laurel, Mont.
By Sunday, Exxon had already stepped up its presence with roughly 120 people involved in efforts to clean up the oil spill.
"We are bringing in experts from across the country to clean up the oil," said Gary Pruessing, ExxonMobil Pipeline Company president, in a statement. "We will stay with the cleanup until it is complete, and we sincerely apologize to the people of Montana for any inconvenience the incident is creating."
On Sunday, air quality monitoring confirmed that there was no danger to public health, and there were no reports of complications with the quality of drinking water.