Meanwhile, OPEC's share of the global oil market will rise to 46% by 2035, when the producers' cartel will need to pump 45.2 million bpd, the IEA said. This compares to a market share of 43% in 2012, when OPEC pumped 37.6 million bpd.

"The share of OPEC countries in global output rises again in the 2020s, as they remain the only large source of relatively low-cost oil," the IEA said.

Saudi Arabia will continue to be OPEC's biggest producer, but Iraq will make up the biggest single contribution to OPEC production growth.

Due to security setbacks and declining output from mature fields, however, OPEC's two North African members, Libya and Algeria, will struggle to boost production capacity over the coming years unless they step up exploration, the IEA warned.

The IEA also raised its estimated global oil demand for 2035, saying it now sees demand expanding by 14 million bpd, to an average of 101 million bpd. In last year's report, the group estimated global oil demand in 2035 would be 99.7 million bpd.

Soaring energy demand in China, India and the Middle East will continue to drive global energy use up by a third over the next two decades, the IEA said.

Crude prices also will rise to $128 per barrel by 2035, helping to support the development of unconventional oil supplies, the IEA said. It said supplies of conventional crude during the period will drop to 65 million bpd.

Global Oil Demand Will Slow

But the group also sees the growth of oil demand slowing steadily, from an average of 1 million bpd per year through 2020 to just 400,000 bpd thereafter. This slowing will be the result of high prices pushing efficiency gains and fuel switching as well as a steady decline in oil use by Organization for Economic Cooperation and Development countries.

The IEA, which expects a drop of more than 40 million bpd in conventional crude output from existing fields between now and 2035, said its analysis of more than 1,600 fields showed that, once production had peaked, an average conventional field could expect to see an annual output decline of around 6%.

Downstream, the IEA estimated nearly 10 million bpd of global refinery capacity is at risk of closure as falling demand in Europe and the U.S. continues to swell overcapacity in the sector.