By Dominic Chopping and Kjetil Malkenes Hovland 

Marathon Oil Corp. is selling its Norwegian business for more than $2 billion in cash to Det Norske Oljeselskap ASA as part of a drive by the Houston-based energy company to sell its North Sea oil-and-gas operations to focus on the U.S.

"The sale of our Norway assets advances one of our key 2014 priorities and further demonstrates our commitment to rigorous portfolio management to simplify and concentrate our business," Marathon Chief Executive Lee M. Tillman said Monday.

In December the company said it would increase in capital spending to boost output while also lifting shareholder returns with a $2.5 billion buyback program.

Marathon said the Norwegian deal was worth $2.7 billion but that after adjustments for debt, net working capital and interest the net proceeds would be $2.1 billion.

Since 2011 Marathon Oil has sold $6.2 billion worth of assets in a bid to improve growth and profitability. It said cash from the Norway deal will be used to promote organic growth and to fund its share buybacks.

However, the company said it had abandoned plans to sell its U.K. North Sea business after failing to attract an acceptable offer.

"Accordingly, we will continue to operate this business as we always have, with a focus on our company's long-held values and commitment to safe and responsible operations," Mr. Tillman said.

For Det Norske Oljeselskap, the acquisition will allow it to bolster capacity as it prepares for production at the massive North Sea field Johan Sverdrup.

The Norwegian company said it expects the deal to be completed in the fourth quarter of 2014, with the plan for development and operation of the Johan Sverdrup field scheduled for submission in February 2015.

"It's a good match," Det norske oljeselskap Chief Executive Karl Johnny Hersvik told The Wall Street Journal. "It provides a basis for a long-term financing solution and a great platform for future growth."

If the Marathon portfolio had been included in 2013, Det norske oljeselskap would have been the eighth-biggest producer in Norway, following state-controlled companies Statoil and Petoro and oil majors Exxon, Total, Shell, Conoco and Eni, according to oil data firm Rystad Energy.

The deal will be funded with a fully underwritten loan and the company also plans to strengthen its finances with a $500 million rights issue, details of which will be announced in mid-July, it said.

J.P. Morgan Limited acted as financial adviser to Det Norske on the transaction.

Write to Dominic Chopping at dominic.chopping@wsj.com and Kjetil Malkenes Hovland at kjetilmalkenes.hovland@wsj.com

Subscribe to WSJ: http://online.wsj.com?mod=djnwires