OPEC forecasts strong global appetite for crude oil in 2018 but now sees output from the United States and elsewhere growing more than previously expected.

The 14-member oil cartel's latest read on supply and demand comes just two weeks after it agreed to extend output limits with Russia and nine other producer nations. The two dozen producers are capping production to shrink huge global stockpiles of oil that have weighed on prices for more than three years.

The higher supply from outside OPEC could make it harder to achieve that aim, even as OPEC's production fell in November.

The producer group on Wednesday forecast that non-OPEC production will grow by nearly 1 million barrels a day in 2018. That marks an upward revision of 120,000 barrels a day from its previous projection.

"Higher-than-expected supply growth in the U.S., Canada and Kazakhstan have been the key contributors to the upward revisions, particularly U.S. tight oil," OPEC said in a monthly report.