Oil slumped 5 percent to near six-year lows on Monday, accelerating its months-long rout after Goldman Sachs slashed its short-term price forecasts and Gulf producers showed no signs of curbing output.
U.S. crude oil closed down $2.29 at $46.07, its lowest since April 2009.
was last down about $3 to $47.24 a barrel, after dropping as low as $47.18, the lowest since March 18, 2009.
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Analysts at Goldman Sachs cut their three-month forecasts for Brent to $42 a barrel from $80 and for the U.S. West Texas Intermediate contract to $41 from $70 a barrel. The bank cut its 2015 Brent forecast to $50.40 a barrel from $83.75 and U.S. crude to $47.15 a barrel from $73.75.
Despite declining investments in U.S. shale oil, the main driver in the current supply glut, production will take longer to come down, Goldman said in a report.
Tariq Zahir of Tyche Capital Advisors said a bottom was hard to predict as prices varied so quickly.
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"I figured we'd see $40 in the near term, but everything seems to be happening quicker than expected," Zahir said. "You're going to get some more margin call selling in here, there will be a bounceback that will be sharp and violent."
Walter Zimmerman of United-ICAP said the market's sharp changes in the last few months make it impossible to predict an average price for the year.
"In today's markets, that are so widely volatile, an average price is completely useless," Zimmerman said.
"There's a million barrels a day of excess production," he said. "That is what is driving the price."
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As OPEC's November decision not to curtail production in the face of falling prices piles pressure on some group members, Venezuelan President Nicolas Maduro met Saudi Arabia's Crown Prince Salman in Riyadh on Sunday as part of a diplomatic tour in the Gulf to discuss falling oil prices.
However, Saudi Arabia, the world's biggest oil exporter, has said it will not support prices by cutting production and ignored calls from smaller OPEC members, including Venezuela, to react to falling oil prices at the cartel's November meeting.
On Saturday, Iran vowed to help Venezuela stem the oil price fall.