Oil production for Organization of the Petroleum Exporting Countries and Russia fell in December, just one month before the group officially starts a new round of output cuts, the organization stated in its monthly report on Thursday.
OPEC struck a deal last month with Russia to cut production by 1.2 barrels per day (bpd) in January, in order to prevent another oil glut.
Oil supplies from OPEC nations dipped 751,000 bpd to nearly 31.6 million bpd, according to independent figures cited by OPEC in its monthly report. Saudi Arabia was the driving force, with output falling by 468,000 bpd to just over 10.5 million bpd in December.
Global oil demand growth for 2019 was unchanged at 1.29 million bpd, while demand for OPEC countries in 2019 is forecast at 30.83 million bpd, down 910,000 bpd from 2018.
Its outlook for non-OPEC output growth was slightly lower, with 2019 supply growth at 2.1 million bpd, outstripping the increase in demand.
After the report, U.S. West Texas Intermediate (WTI) crude futures slumped 1.59% to $51.53 a barrel by 7:01 AM ET (12:01 GMT).
Brent crude futures, the benchmark for oil prices outside the U.S., fell 1.21%, to $60.58 a barrel.