Slowing global economic growth together with robust output from Opec producers will mean the oil market glut will persist through 2016, the world’s leading energy forecaster said on Tuesday.

The International Energy Agency said in its closely watched monthly report a “marked slowdown” in oil demand growth looms as the stimulus from lower prices fades and economic activity weakens in countries dependent on commodity revenues.

At the same time, despite the oil price plunge curbing growth in US shale and other non-Opec production, additional barrels from Iran — alongside others within the producers’ group — will ensure the oil overhang remains into next year.

A collapse in oil prices has supported strong oil demand growth this year. But the IEA anticipates oil demand growth will fall to 1.2m barrels a day in 2016 — to 95.7m b/d — down from initial estimates of 1.4m b/d. It is a sharp contrast to the stronger than expected 1.8m b/d in 2015, taking total demand to 94.5m b/d.

The IEA, which uses the International Monetary Fund’s growth assumptions for its oil demand estimates, said the global economic outlook was “more pessimistic”. The fund said earlier this month the world economy will for 2015 expand at its slowest pace since the global financial crisis.

The world’s top consumers such as the US and China increased crude purchases this year as oil at 6½-year lows drove gasoline demand, the IEA said. But the “lower price-driven exuberance” is waning amid “expectations that crude oil prices will not see repeats of the heavy losses of 2015”, it added.

Weaker economic growth in oil-dependent economies such as Canada, Brazil, Venezuela, Russia and Saudi Arabia will also have an impact on demand growth. “Lower commodity prices, with all else held equal, eventually equate to lower public spending and a potential dampening in consumer expenditure in many of these countries,” the IEA said.

World oil supply held steady near 96.6m b/d in September as a drop in output from the US, and other producers outside of Opec, was offset by increased supply from the cartel itself.

“High-cost supply — primarily non-Opec — is being forced out,” the IEA said. “Supply in the US — which had been the motor of growth — is already sinking swiftly.”

Non-Opec supply slipped 180,000 b/d to 58.3m b/d in September as spending cuts of more than 20 per cent by the world’s biggest energy companies have an impact on new projects and existing output. Production is expected to average at this level for 2015, before dropping to 57.8m b/d next year as lower oil prices continue to bite.

“The sharpest slowdown is in the US,” the IEA said. “Further reductions in drilling activity since the start of September are expected to accelerate declines in US light tight oil production.”

US year-over-year gains have eased to just 300,000 b/d from 1.6m b/d in early 2015.

Non-Opec supplies nevertheless exceeded expectations, with Brazil and Russia recording record output levels during August and September.

Opec crude supply — led by record Iraqi output which offset declines from Saudi Arabia — rose 90,000 kb/d in September to 31.7m b/d. Year to date the group has pumped 31.2m b/d, 1m b/d higher than the same period a year ago.