Global energy demand is set to skyrocket over the next two decades, OPEC said in its latest annual outlook, with India and China the most important contributors to this growth.

In the influential oil cartel’s 2018 World Oil Outlook (WOO), the group said it expects total primary energy demand to surge around 33 percent from 2015 levels.

Driven almost entirely by developing countries — most notably India and China — demand is expected to increase at an average annual growth rate of nearly 2 percent, reaching 365 million barrels per day (bpd) in 2040, according to CNBC. „Energy demand in India and China in this period is forecast to increase by 22 million bpd and 21 million bpd, respectively, which is more than 50 percent of the energy demand growth in developing countries during this period,” OPEC said in the report.

At present, energy market participants are increasingly concerned about a slowdown in the global economy, escalating trade tensions, emerging market countries’ currency weakness and the potential fallout this could have on oil demand.

Last month, the International Monetary Fund (IMF) cut its outlook for the world economy in 2018-19 by 0.2 percentage points to 3.7 percent. Fears of a slowdown in global growth, and by extension oil consumption, have prompted sharp falls in equity and crude prices in recent weeks.

Yet, while oil consumption threatens to disappoint energy market participants on the downside, production in U.S. shale fields continues to defy expectations. This, in turn, has reinforced the market management challenge for OPEC and its partners.

Saudi Arabia’s Energy Minister Khalid al-Falih said Monday that OPEC and its allies had conducted an analysis which showed a 1 million bpd drop in crude supplies from October levels could soon be required to balance the market. „We have underestimated U.S. shale … And now we are at risk of underestimating it again but collectively as a group, we understand shale better than before. Still, it continues to surprise us on the upside,” Ayed Al-Qahtani, director of research at OPEC, said at an industry event at ADIPEC oil summit in Abu Dhabi on Tuesday.