Exxon Mobil contractors clean up oil along the banks of the Yellowstone River in Billings, Mont.
"We will continue to add resources and are extremely grateful for the patience and assistance of local residents and authorities," Pruessing said on Sunday.
By Monday, Exxon reported that more than 280 people were involved in cleanup efforts.
Crews had used about 2,300 absorbent pads that measured more than 48,000 feet to soak up oil that had washed to shorelines. Exxon had also deployed vacuum tankers to suck the oil from the river.