Today’s oil market is suffering from an abundance of crude supplies that is pushing prices to painful lows for producers. But the industry could soon face the opposite problem: Too little supply to match the world’s demand, researchers said.

The collapse in crude prices over the past two years has forced oil and gas companies to slash their budgets, cancel billions of dollars in exploration projects and hone their focus on existing wells. At the same time, newer discoveries in recent years have yielded disappointing results.

The global oil market could face a supply shortfall of 4.5 million barrels a day within the next two decades, Wood Mackenzie, a global energy consulting firm in Scotland, said Wednesday in a report. That’s down from today’s estimated surplus of around 2 million barrels a day.

“Unless exploration results start to improve significantly, continued supply growth will become unsustainable,” Patrick Gibson, director of global oil supply research at Wood Mackenzie, said in a statement.

The researchers surveyed the more than 7,000 conventional oil fields discovered since 2000. They found that the volume of liquids discovered each year more than halved in the past decade as wells turned up less crude than anticipated. Volumes fell from around 19 billion barrels in the 2008-11 period to around 8 billion barrels in the 2012-15 period, the report said.

In the medium term, oil supplies will still be sufficient to meet the world’s demand. Around 90 percent of the oil from recent finds has yet to be produced, and the industry continues to find ways to squeeze more supplies from unconventional fields, such as U.S. shale formations and offshore, deep-water developments. 

But spending cuts throughout the sector could jeopardize longer-term production, the researchers said.

With oil prices down nearly 60 percent from their June 2014 peak of over $100 a barrel, energy giants from BP to Exxon Mobil and Schlumberger have announced massive reductions in their capital expenditures and exploration plans. Oil companies cut investment spending by more than $100 billion in 2015, and another round of major cuts is expected in 2016, the International Energy Agency estimated.

Wood Mackenzie said it expects the industry to invest $40 billion per year in exploration and appraisal 2016 to 2018, or less than half the sector’s investment 2012 to 2014. That means as existing reserves dwindle and new discoveries disappoint, the sector isn’t investing enough to replace those supplies, the researchers said.

“We forecast that by 2030, production from fields discovered since 2000 will be in decline,” Gibson said. He added if the current annual average of 8 billion barrels of discovered liquids continues, the industry could see a shortfall of 4.5 million barrels a day by 2035.

“That is why the size and nature of the next tranche of discoveries is crucial for maintaining long-term global oil supply growth,” he said.