April 18 (Bloomberg) -- Refineries in the U.S. Midwest run by Marathon Oil Corp., Valero Energy Corp., BP Plc, Exxon Mobil Corp. and CountryMark Cooperative were unaffected by an early morning earthquake in Illinois.

Marathon, the largest refinery in the Midwest, shut its Potoka crude-oil pipeline as a precaution after the earthquake struck, Linda Casey, a company spokeswoman, said in a telephone interview. The line has returned to service and is operating normally she said.

Marathon's 213,000 barrel-a-day refinery in Robinson, Illinois, about 40 miles north of the earthquake's epicenter, was unaffected by the quake, she said.

``I've gotten a lot of calls from people asking if there was any impact, but we don't see anybody out buying product for the weekend because of it, so I don't think there was an impact,'' said Steve Mosby, vice president of ADMO Energy LLC, a supply consultant in Kansas City, Missouri.

Valero's Memphis, Tennessee, refinery was also unaffected, Bill Day, a company spokesman, said in a telephone interview. The refinery has a daily processing capacity of 182,000 barrels, according to the Energy Department.

BP's 420,000 barrel-a-day refinery in Whiting, Indiana, ``is operating normally,'' Scott Dean, a company spokesman, said in a telephone interview.

Exxon's Joliet, Illinois, refinery near Chicago was unaffected, said Prem Nair, a company spokeswoman. The refinery can process 248,500 barrels a day, according to the Energy Department.

There was also no impact on CountryMark's Mount Vernon, Indiana, refinery, said John Deaton, the company's senior vice president. The plant, about 35 miles south of the epicenter, can process 23,500 barrels of oil a day.

To contact the reporter on this story: Jordan Burke in New York at jburke29@bloomberg.net; Barbara Powell in Dallas at Bpowell4@bloomberg.net.

Last Updated: April 18, 2008 13:40 EDT