The exploration and production company Marathon Oil said on Monday that it would sell its North Sea oil business in Norway to a Norwegian oil producer for $2.1 billion in cash.

Marathon, based in Houston, also said it had called off the sale of its British business after failing to receive what it deemed an acceptable offer.

The Norwegian sale, to Det Norske Oljeselskap, is the latest move in an effort by Marathon to streamline its portfolio of assets.

Like other midsize American oil companies, Marathon has been under pressure to trim its overseas activities and invest more in the United States, where oil and gas production is booming. Investors also worry about political risk outside the country.

Marathon’s sale of Norwegian assets is the latest milestone in the company’s effort to refocus its activities. Since 2011, Marathon has agreed asset sales worth $6.2 billion, including the sale of a $1.5 billion stake in an Angolan oil field last year.

Marathon is putting the money from the sales into a combination of American shale oil investments and share buybacks.

“The disciplined allocation of capital to opportunities that can deliver long-term growth at higher returns and improved margins is a strategic imperative,” Lee M. Tillman, the president and chief executive of Marathon, said in a statement.

The sale announced on Monday includes a floating production, storage and offloading vessel operated by Marathon as well as various production licenses in the North Sea, Marathon said. In 2013, its production in Norway averaged the equivalent of about 80,000 barrels of oil a day.

Det Norske said the transaction would complement its planned production in the Ivar Aasen and Johan Sverdrup fields in the North Sea and that it would have about 200 million barrels of oil equivalent in proven reserves and probable deposits after the transaction.

The deal is subject to regulatory approval and is expected to close in the fourth quarter.

Det Norske’s strategy has been to create a strong Norwegian exploration and production company, said Sverre Skogen, the Det Norske chairman. “With this transformational transaction we have achieved our goal well ahead of schedule.”

Production has been slowing in the North Sea, although to a greater extent in British than in Norwegian waters.

The Norwegian oil and gas industry has had considerable success moving north and making new finds, although this direction is raising increasing concerns about the potential to damage sensitive environments.

The 80,000 barrels of oil equivalent production that Marathon is selling is only a tiny portion of overall Norwegian output.

American companies like the Apache Corporation, based in Houston, and the Hess Corporation, based in New York, also have been putting assets on the block to reduce overseas exposure and raise money for investment at home.

In April, for instance, Hess said it was selling its interests in two Thai fields to PTT Exploration and Production of Thailand for $1 billion. Last year, Hess sold assets in Indonesia for $1.3 billion and in Russia for about $2 billion.

Earlier this year, Apache sold its Argentine business for $800 million. Last year, it bowed to investor complaints about the riskiness of its very profitable Egyptian business and sold about a third of its operations there to Sinopec of China for about $3 billion.

Marathon had also been seeking to sell its British North Sea business but it said on Monday that it had ”received no acceptable offer” for these stakes and so would retain them.

With so much for sale, it may be growing difficult to find buyers.

The New York Times