After a day of talks in Vienna, OPEC and non-OPEC producers led by Russia decided to prolong their -1.80 million barrels a day output reduction for an additional duration of nine months, extending a deal that was due to expire in March. The decision confounded oil analysts, who had expected Moscow to be more insistent on a shorter pact amid fears of a ramp-up in production by US shale operators. Saudi Oil Minister Khalid al-Falih said the group would review the progress of the deal at its next meeting in June, with the option to exit early if the market overheated. West Texas Intermediate crude futures for January delivery are gaining early Friday to last trade around the $57.65-zone per barrel. Since the agreement came in to force a year ago, global inventories have slipped, helping crude prices rally by more than $20.00 a barrel.