Norwegian energy group Statoil said Monday it had made a 4.4-billion-dollar bid for US group Brigham Exploration, which has stakes in North Dakota and Montana, reported dpa.
Statoil chief executive Helge Lund said the bid was in line with the state-controlled group's strategy to be "a leading player in the fast growing US onshore oil and gas industry."
At present, production in the "tight oil" fields in the Williston Basin is estimated at 21,000 barrels of oil equivalent a day, but could potentially increase to between 60,000 and 100,000 barrels a day over a five-year period, Statoil said.
Tight oil reservoirs can consist of shale or other so-called tight rocks, which are not very porous and therefore difficult to extract oil from.
The bid of 36.50 dollars per share was backed by Brigham Exploration's board, which owns 2.5 per cent of the Texas-based group. According to Statoil the bid was a 36-per-cent premium on the average share price in the past 30-day period.
The deal was expected to be completed during the first quarter of 2012.