* U.S. firm considering selling all or part of its UK assets
* British North Sea portfolio valued at up to $2bln
* Exxon focusing on U.S. shale and new projects(Adds background, graphic)
By Ron Bousso
LONDON, Aug 13 (Reuters) - Exxon Mobil isconsidering an exit from the British North Sea after more than50 years in the oil and gas basin as it focuses on U.S. shaleproduction and new projects.
The world's largest publicly traded energy company, Exxonhas held talks with a number of North Sea operators in recentweeks to gauge interest in some or all of its assets, whichcould fetch up to $2 billion, according to three industrysources with knowledge of the matter.
Exxon declined to comment.
Leaving the British North Sea would mark a major retreatfrom Europe for Irving, Texas headquartered Exxon, which hasalready put its Norwegian offshore assets on the block.
It would follow similar moves by U.S. rivals Chevron andConocoPhillips which earlier this year sold the bulk of theirNorth Sea operations.
Most of Exxon's operations are managed through a 50-50 jointventure with Royal Dutch Shell, known as EssoExploration and Production UK, and include interests in nearly40 oil and gas fields.
Shell declined to comment.
Exxon produces around 80,000 barrels of oil and 441 millioncubic feet of gas a day in the British North Sea, according toits website.
Potential buyers could include large private equity-backedNorth Sea producers such as Chrysaor or Neptune which haveacquired portfolios from veteran producers in recent years.
Assigning a value to oil and gas assets in the North Sea iscomplicated because many fields and infrastructure are nearingthe end of their lives and require dismantling, ordecommissioning, an expensive process which can offset years ofproduction revenue.
The North Sea has seen a revival in production in recentyears, however, due to new fields coming on line and improvedperformance by operators following the 2014 oil price collapse.
Still, the basin's production is expected to decline overthe next decade, according to the U.K. Oil and Gas Authority.
Should the direct discussions with potential buyers notyield a result, Exxon will consider appointing an external bankto run a formal sale process, two of the sources added.
It was unclear if a sale of asset would require breaking upthe Esso joint venture.
Esso has been producing gas since 1968 and oil since 1976including from the Brent field, which is eponymous with theglobal crude benchmark and is now being decommissioned.
Exxon's operational focal point in recent years has turnedto the United States, where it is rapidly ramping up oilproduction in the Permian Basin, as well as in Guyana, where itis developing huge, untapped fields.
(Additional reporting by Gary McWilliams in Houston; editing byJason Neely)
