OPEC expects global oil markets to tip into a surplus as the I.E.A. boosted its forecast for global demand growth this year. Elizabeth Low reports. Oil headed for the biggest weekly gain in about four months on interruptions to supply and speculation fuel switching will buoy demand. West Texas Intermediate traded near $94 a barrel, up by more than 5% this week. Six oil and gas fields in the Gulf of Mexico were shut after a leak at a Louisiana booster station halted two pipelines. The conduits are expected to resume service on Friday, according to Shell Plc. The International Energy Agency boosted its forecast for global demand growth as soaring natural gas prices and heat waves spur demand. The agency saw consumption 380,000 barrels a day higher than its previous forecast. Wider markets have been on a firmer footing this week after US inflation figures missed expectations, […]