Fire departments in Billings and Lockwood, Montana, responded to the scene, the Billings Fire Department tweeted.
As of early Sunday morning, no injuries had been reported, an ExxonMobil spokesperson told CNN affiliate KULR.
CNN reached out to ExxonMobil for additional details.
The refinery is located on the bank of the Yellowstone River near Lockwood, Montana, according to the ExxonMobil website.
It covers 720 acres, which includes about 370 acres of undeveloped land and urban wildlife habitat area, according to the website.