Oil prices fell on Thursday after rebounding 8 percent in the previous session, with futures pressured by concerns over a faltering global economy and worries about a glut in crude supply.
Prices surged on Wednesday, tracking heavily with a spike in the U.S. equities market after President Donald Trump's administration attempted to shore up investor confidence.
However, U.S. stocks retreated on Thursday, dragging oil prices down with them.
"In the absence of major oil specific headlines, the petroleum complex has become 'attached to the hip' of the equities amidst this week's extreme price moves that have been developing in both directions," Jim Ritterbusch, president of Ritterbusch and Associates, said in a note.
Both Brent and WTI have lost more than a third of their value since the beginning of October and are heading for losses of more than 20 percent in 2018.
"Fear of a bear market remains in place," said Johannes Gross at Vienna-based consultancy JBC Energy.
Concerns about slowing global economic growth have dampened investor sentiment in riskier asset classes and pressured crude futures.
Market participants have grown worried about an oversupply of crude. Three months ago it looked as if the global oil market would be undersupplied through the northern hemisphere winter as U.S. sanctions removed large volumes of Iranian crude. But other oil exporters have compensated for any shortfall, filling global inventories and depressing prices.
OPEC met earlier this month with other producers including Russia and agreed to reduce output by 1.2 million barrels per day, equivalent to more than 1 percent of global consumption.
But the cuts won't take effect until next month and oil production has been at or near record highs in the United States, Russia and Saudi Arabia, with the U.S. pumping 11.6 million bpd of crude, more than both Saudi Arabia and Russia.
Russian Energy Minister Alexander Novak said on Thursday that the country will cut its output by between 3 and 5 million tonnes in the first half of 2019 as part of the deal. It then will be able to restore it to 556 million tons (11.12 million barrels per day) for the whole 2019, on par with 2018, he added.
Although U.S. sanctions have put a cap on Iran's oil sales, Tehran has said its private exporters have "no problems" selling its oil.
"Markets need more concrete evidence on improving fundamental metrics and to bring the supply-demand relationship back to balance before oil prices can reach a real bottom," said Margaret Yang, market analyst for CMC Markets.
Data on the U.S. market will appear in the next couple of days with figures from the American Petroleum Institute on Thursday and a report from the U.S. Energy Information Administration on Friday.
A Reuters survey estimated that U.S. crude inventories dropped 2.7 million barrels in the week to Dec. 21.