When OPEC, Russia and their allies agreed in April to slash oil production, little did they expect that their initiative to prop up collapsing prices would be helped by a swift drop in U.S. output. Now that crude has rallied on the back of those cuts from below $20 a barrel to $40 or more, the group known as OPEC+ faces a fresh challenge: stopping U.S. shale production delivering another surprise by recovering equally quickly. “The plan is to stick to prices of $40-$50 per barrel because as soon as they rise any further to say $70 per barrel it encourages too much oil production, including U.S. shale,” said a Russian source familiar with OPEC+ talks on the issue. OPEC+ sources told Reuters on Wednesday that Russia and Saudi Arabia had reached a compromise to extend into July the group’s existing output cuts of 9.7 million […]