U.S. oil major Exxon Mobil Corp. has hired investment bank Jefferies to sell the stakes it holds in oil and gas fields off the Norwegian coast, which could fetch up to $4 billion, banking sources said.

Exxon Mobil said in June that it was looking to test market interest for its Norwegian upstream portfolio, which includes minority stakes in more than 20 other fields, operated by local producer Equinor ASA and Anglo-Dutch oil major Royal Dutch Shell Plc.

The bank has now instructed Jefferies to help with the process, three sources said, to accelerate its exit from the northern European country where it has been operating for more than 125 years.

Interested parties are expected to receive a presentation of the available assets later in August, one of the sources said.

Exxon Mobil and Jefferies declined to comment.

A number of private equity-backed firms, including Okea ASA, and independent oil companies Aker BP ASA and DNO ASA, have said they were looking to buy more assets on the Norwegian Continental Shelf.

Var Energi AS, jointly owned by Italy's Eni SpA and Norwegian private equity fund HitecVision AS, is likely to show an interest, having previously bought Norwegian assets from Exxon Mobil in 2017, a second source said.

The North Sea offshore basin, which started production in the 1970s, has undergone a broad change of guard in recent years as veteran producers have been replaced by smaller players that say they can squeeze more oil and gas from the fields.

U.S. major Chevron Corp. transferred its last stake in a Norwegian offshore license last year, while ConocoPhillips Co. still operates Ekofisk, the first big oil discovery off Norway.

In 2017, Exxon Mobil's net production from fields off Norway was about 168,000 barrels of oil equivalent per day. Its total net reserves in the producing fields stood at 422 million barrels of oil equivalent by the end of 2018.