MDU Resources Group, Inc. (NYSE: MDU) through its wholly owned subsidiary, WBI Holdings, Inc. (WBI) and Calumet Refining, LLC, an entity owned by the existing owners of the general partner of Calumet Specialty Products Partners, L.P. (NASDAQ: CLMT) (“Calumet”) today announced they have signed a nonbinding letter of intent to explore the feasibility of jointly building and operating a 20,000 barrel per day diesel refinery in southwestern North Dakota. The facility would process Bakken crude and market the diesel within the Bakken region. Site selection, permitting, crude oil feed procurement, marketing and engineering studies are currently underway. Upon successful completion of the project, Calumet Refining, LLC expects to contribute its interest in the joint venture to Calumet in exchange for cash and/or partnership interests. “This project will capitalize on the capabilities and expertise of two strong companies to develop a facility that will serve demand for diesel by agriculture and industry in the rapidly developing Bakken play ,” said Terry D. Hildestad, president and chief executive officer of MDU Resources . “We believe this joint venture will add value to Bakken crude. It will provide value to southwestern North Dakota communities by providing steady, good-paying, long-term jobs and through the two companies’ longstanding commitment to the communities in which they operate and serve.” “We are excited that the owners of our general partner are partnering with MDU Resources and WBI to explore refining opportunities in the Bakken ,” said Jennifer G. Straumins, president and chief operating officer of Calumet’s general partner. “We believe that our refining capabilities and their operating experience in the Bakken would be a strong combination. Both companies provide operational expertise and capability vital to the success of a large industrial project similar to this planned facility.” Hildestad said the project exemplifies the potential that exists for all of the major subsidiary companies within MDU Resources to participate in a value-added project in the Bakken region and elsewhere.