* Statoil, Brigham agree $36.50 per share all-cash offer

* Deal gives enterprise value of some $4.7 bln

* Statoil sees break-even production price of $55/barrel

* Bingham Exploration shares jump 20 pct to $36.36

By Gwladys Fouche

OSLO, Oct 17 (Reuters) - Statoil is paying $4.4 billion for Brigham Exploration to boost its unconventional energy resources in the United States, one of its key growth areas.

The Norwegian state-controlled oil firm backed its belief in the growing importance of unconventional sources on energy supplies with an agreed $36.50 per share all-cash offer, a 36 percent premium to Brigham's average price in the past month.

Statoil already has a stake in the Marcellus shale gas project with Chesapeake in north-east America and owns acreage in the Eagle Ford prospect in Texas, together with Canada's Talisman .

"Marcellus is primarily dry gas, Eagle Ford is a combination of dry gas and liquids and this (Brigham's assets) is oil. We now have a good, deep position in the U.S. in unconventionals," said Statoil Chief Executive Helge Lund.

Brigham shares jumped 20 percent to $36.36 on the Nasdaq bourse. The deal estimates an enterprise value of $4.7 billion for Brigham, Statoil said.

North America has in recent years seen a boom in energy resources such as shale gas, raising the prospect that the world's largest economy may lower its dependence on imported energy.

"We are seeking positions in the most competitive plays within unconventionals in the U.S.," Lund told Reuters. "We believe unconventional resources will be more and more important for future energy supplies."

Statoil sees the United States as one of its key growth areas outside of its home region and is a major holder of deepwater licences in the Gulf of Mexico.

Terra analyst Irmantas Vaskela said the acquisition price was good, assuming Statoil can produce the oil for less than $55 per barrel, as indicated.

"If the (break-even) calculations are right then it is a good price," he said. "And it's quite a big deal for Statoil."

The Brigham deal would allow Statoil to become an operator in unconventional energy quickly, something the firm is already seeking to do with the development of the Eagle Ford play.

Lund said he saw the deal as part of Statoil's aims to focus increasingly on upstream activities, such as production and exploration, rather than refining and sales.

"This is part of our focus on production," Lund told reporters. "We do not rule out further acquisitions."

Several big oil companies have in recent years sold off big chunks of their retail or refining operations to focus on the more lucrative sectors of finding and producing oil and gas, the latest of which was ConocoPhillips in July.

Statoil has spun off its petrol stations business but still had a refining division where margins have more than halved in a year.

OUTPUT POTENTIAL SEEN UP TO 100,000 BARRELS/DAY

Austin-based Brigham's assets in the Williston Basin in North Dakota and Montana, which include the Bakken and Three Forks oil plays, include an estimated resource base of 300 million to 500 million barrels of equity-based oil equivalent (boe).

Current equity production is some 21,000 boe per day.

The acreage, which mostly consists of "tight oil", has potential to ramp up to 60,000 to 100,000 boe per day equity production over a five-year period, Statoil said, adding the transaction was expected to close in the first quarter of 2012.

Tight oil is one of the many types of unconventional energy resources that the industry has been developing in recent years using new techniques.

"This is in line with Statoil's strategy of expanding in the United States in unconventional oil," Terra's Vaskela said, noting "tight oil" reserves such as Brigham's require much the same hydraulic fracturing technology used in shale-gas recovery.

Another analyst said Statoil was seeking to balance its portfolio.

"To me, the land-based investment work is a strategic hedge against North Sea exposure. These assets will last for many years," said analyst Helge Andre Martinsen at Nordea Markets.

"I take a balanced view. There are many sceptics but it will take 30 years before you know if it was the right thing to do."

Lund, who declined to say whether he expected rival bids to emerge, said Statoil and Brigham had been working on the deal for almost a year.

"We know the company well. We have a bid that reflects the valuation of the company," he said.

Shares in Statoil closed down 0.44 percent at 137.42 crowns while the Oslo benchmark index was down 0.76 percent.