Oil prices fell into the red in late afternoon trading on Wednesday after the CDC confirmed the firm omicron case in the U.S.
Brent crude futures for February slid 0.2% to $69.08 per barrel.
U.S. West Texas Intermediate (WTI) crude futures fell 0.4% to $65.90 per barrel. Both contracts retraced some of their gains after an OPEC+ document showed the group forecasting a bigger oil surplus in the new year than previously thought.
Both Brent and WTI front-month contracts in November posted their steepest monthly falls in percentage terms since March 2020, down 16% and 21% respectively.
The Organization of the Petroleum Exporting Countries met on Wednesday ahead of a meeting on Thursday of OPEC+, which groups OPEC with allies including Russia.
OPEC+ sees the oil surplus worsening to 2 million barrels per day (bpd) in January, 3.4 million bpd in February and 3.8 million bpd in March next year, an internal report seen by Reuters showed.
Some analysts expect OPEC+ to pause plans to add 400,000 bpd of supply in January.
"There is much to suggest that OPEC+ will not initially step up its oil production any further in an effort to maintain current prices at around $70/bbl," PVM analyst Stephen Brennock said.
"OPEC+ have erred on the side of caution since it began slowly boosting supplies and a decision to shelve a planned increase output in January and keep its quota flat comports with its cautious approach."
Several OPEC+ ministers, though, have said there is no need to change course.
But even if OPEC+ agrees to go ahead with its planned supply increase in January, producers may struggle to add that much.
A Reuters survey found OPEC pumped 27.74 million bpd in November, up 220,000 bpd from the previous month, but that was below the 254,000 bpd increase allowed for OPEC members under the OPEC+ agreement.
In a bearish sign for demand, data from the American Petroleum Institute industry group showed U.S. crude stocks fell by 747,000 barrels in the week ended Nov. 26, according to market sources, a smaller decline than expected.
Government stockpile data is due at 1530 GMT.