Chevron said it is set to launch the sale of its remaining UK North Sea oil and gas assets, in a move that would mark the U.S. energy giant's exit from the ageing basin after more than 55 years. The planned divestment, confirmed to Reuters on Thursday, comes as Chevron prepares for the $53 billion acquisition of rival Hess which it previously said will include $10 billion to $15 billion in asset sales around the world. The exit will be the latest step in a steady retreat of top oil and gas companies from the declining British basin which pioneered deepwater production in the 1970s, as they focus on newer assets around the world.