MDU Resources Group, Inc. (NYSE:MDU) today announced the acquisition of 20,000 additional acres of leaseholds in the Bakken oil play. The new leaseholds are in Richland County, Montana. The company now holds a total of approximately 90,000 net acres of leaseholds in the Bakken.Richland County, Montana, is where the current Bakken play began back in 2000.