Oil is headed for its biggest weekly gain in 15 months after OPEC approved its first supply cut in eight years, with attention now shifting to the deal’s implementation and how producers outside the group will react to any price rally. Futures were little changed in New York and poised for an 11 percent weekly gain. OPEC’s three largest producers — Saudi Arabia, Iraq and Iran — overcame disagreements to reach Wednesday’s pact to reduce the group’s output by 1.2 million barrels a day, while Russia pledged a cut of as much as 300,000. The deal will accelerate the decline of global stockpiles, Secretary-General Mohammad Barkindo said in a Bloomberg TV interview Thursday. The Organization of Petroleum Exporting Countries set a collective output target at the lower end of the range outlined two months ago in Algiers, sending oil prices above $50 a barrel and prompting predictions of a […]