Dec 8, 2014, 7:12am MST Kathleen Lavine | Denver Business Journal

Jim Volker, the head of Whiting Petroleum, announced the closing of the company's purchase of Kodiak Oil & Gas.

Denver's Whiting Petroleum Corp. on Monday has completed its purchase of Kodiak Oil & Gas Corp.

The deal creates the largest crude-oil producer in the bountiful Bakken shale region of the northern Great Plains. The combined company has a market cap of about $6.2 billion.

Whiting (NYSE: WLL) and Denver-based Kodiak (NYSE: KOG) have been working toward the all-stock deal since July. Whiting shareholders gave their approval last week.

"We are excited to move forward as one company that is even betterpositioned to deliver value to our stockholders, customers and employees," James Volker, Whiting's chairman, president and CEO, said in a statement. "Uniting our complementary acreage positions and substantial inventory of high return drilling locations provides Whiting with an expanded platform for growth."

Lynn Peterson, who was Kodiak's president and CEO, and Jim Catlin, an executive vice president and director of Kodiak, will join the Whiting board.

Each share of Kodiak stock will be exchanged for 0.177 of a share in Whiting.