Higher oil output from Opec and a slowdown in world economic growth means the crude oil glut will persist through next year, the world’s leading energy forecaster said on Tuesday. The International Energy Agency said it expected a “marked slowdown” in oil demand growth as the stimulus from lower prices faded and as economic activity weakened in countries dependent on commodity revenues. “Oil at $50 a barrel is a powerful driver in rebalancing the global oil market,” the IEA said in its closely watched monthly report. “But a projected marked slowdown in demand growth next year and the anticipated arrival of additional Iranian barrels . . . are likely to keep the market oversupplied through 2016.” An increase in production from Opec member Iran once sanctions are lifted is expected to overshadow the first drop in US oil output since 2008, the IEA added. The collapse in oil prices has supported the strongest oil demand growth in almost a decade, with low prices helping boost demand by 1.8m barrels a day to 94.5m b/d. Gasoline demand has been particularly strong, suggesting motorists have been encouraged to drive more by lower prices. But the IEA forecasts that effect will fade, with demand growth set to slow to 1.2m b/d next year.