Meeting the world’s energy supply needs by 2035 will require $40 trillion of investment, as demand grows and production and processing facilities have to be replaced, the International Energy Agency (IEA) said, according to Bloomberg June 3.

More than half of that amount will be needed to compensate for declining output at mature oil and gas fields, and the remainder on finding new supplies to meet rising demand, the Paris-based agency said in a report June 3. The world will increasingly rely on countries that restrict foreign companies’ access to their oil reserves, as North American shale output tails off from the middle of next decade, it predicted.

“Declines and retirements set a major reinvestment challenge for policy makers and the industry,” said the IEA, which advises 29 of the most industrialized nations on energy policy. “In the case of oil, the focus for meeting incremental demand shifts towards the main conventional resource holders in the Middle East as the rise in non-OPEC supply starts to run out of steam in the 2020s.”

While a boom in shale oil is pushing U.S. production to its highest level in almost 30 years, diminishing the biggest crude consumer’s reliance on imports, this output surge is forecast to fade, restoring the importance of supplies from the Middle East and OPEC.

Spending on extracting oil and gas worldwide will climb by 25%, to $850 billion a year by 2035, with most of this concentrated in natural gas, according to the report. Global markets will tighten if investments in the resource-rich Middle East are too slow, pushing oil prices $15 a barrel (bbl) higher on average in 2025, it warned. Brent futures averaged $108.70/bbl last year.

“The prospects for a timely increase in oil investment in the Middle East are uncertain,” according to the agency, which estimates that more than 70% of global oil and gas reserves are under the ownership of state-controlled entities. OPEC, whose largest producer is Saudi Arabia, currently accounts for 40% of global oil supplies.

“Decisions to commit capital to the energy sector are increasingly shaped by government policy measures and incentives, rather than by signals coming from competitive markets,” according to the IEA.

About half of the $40 trillion spent on energy through 2035 will be on extraction, refining and transporting fossil fuels, the report indicated. Two-thirds of the total will be spent in emerging economies, according to the agency. Investment needed in renewable energy will total $6 trillion, with another $1 trillion in nuclear power.

Annual spending on satisfying global energy requirements will increase to $2 trillion by 2035, up from $1.6 trillion last year, the agency projected.

Spending on energy efficiency through 2035 pushes the total required investment to $48 trillion, according to the IEA.