"Breathing space" in global crude oil markets ushered in by U.S. shale oil output doesn't mean the glut will last forever, the IEA said in a Wednesday report.

The International Energy Agency said in its annual report oil supplies rise globally to 104 million barrels per day by 2040. The poles of demand, meanwhile, shift to Central Asia and the Middle East, which eventually take over after Chinese and U.S. demand levels out.

IEA Chief Economist Fatih Birol said there are challenges ahead in terms of meeting expected global oil demand despite recent trends from North America.

"The apparent breathing space provided by rising output in the Americas over the next decade provides little reassurance, given the long lead times of new upstream projects," he said in a statement.

The U.S. Energy Information Administration said in its latest monthly report total crude oil production averaged 8.7 million barrels per day in September, the highest monthly level in more than a quarter century. If realized, the 2015 forecast of 9.5 million bpd would be the highest annual average level since 1970.

That level of production has ushered in a sea change in a global oil market once swayed by the output from the Organization of Petroleum Exporting Countries. In its market report for November, OPEC said oil supply from producers outside the 12-member group grows by 1.24 million bpd next year, with North America in part leading the way.

"In October, OPEC crude oil production averaged 30.25 million bpd, according to secondary sources, a decrease of 230,000 bpd from the slightly upwardly revised September figure of 30.48 million bpd," the November report read.

IEA warns, however, the growth in U.S. shale oil production "levels off" by the next decade and Middle East producers once again take the lead as the major source of new oil supplies.

"A well-supplied oil market in the short-term should not disguise the challenges that lie ahead, as the world is set to rely more heavily on a relatively small number of producing countries," Birol said.