Whiting, which has headquarters in Denver, acquired Kodiak in an all-stock transaction valued at $6 billion. Whiting in a statement said the transaction creates the largest regional producer with more than 107,000 barrels of oil equivalent per day of production in first quarter 2014.
Whiting Chief Executive Officer James Volker said he expects total 2014 production from the transaction to reach 152,000 boe per day and have proved reserves of 606 million boe, of which 80 percent is oil.
Kodiak last year spent $660 million in cash to acquire 42,000 acres in the Bakken and Three Forks areas of the Williston Basin of North Dakota from rival Liberty Resources.
North Dakota's government said oil production in April, the last full month for which data are available, was 1,001,149 barrels of oil per day, the first time output passed 1 million bpd in the state.
More than 90 percent of the oil produced came from the Bakken and Three Forks area.