Oil fell for a third day to around $80 a barrel on Monday, extending its retreat from last week's one-year high, on renewed concerns about the strength of the global economy.
Weak U.S. industrial sector earnings last week pushed down stock markets and underscored concerns about the pace of the U.S. economic recovery and its impact on energy demand.
It's profit-taking after the surge in the past week without any change in fundamentals, said Carsten Fritsch, analyst at Commerzbank, of the price fall.
There's more bearish factors than there is support from financial markets, he said, adding that oil could quickly resume its rally given more support from outside factors such as equities.
U.S. crude for December delivery fell 32 cents to $80.18 by 1021 GMT (6:21 a.m. EDT), having earlier fallen as low as $79.57. It reached a 2009 high of $82.00 on October 21. Brent crude fell 17 cents to $78.75.
The market is cautious about pushing oil prices higher because the demand fundamentals are still weak and the world economy is still fragile, said Ryuichi Sato, an analyst at Mizuho Corporate Bank.
Adding to bearish sentiment, Nigeria's main militant group reinstated a ceasefire on Sunday in the oil-producing Niger Delta to allow for peace talks with the government.
Attacks on oil installations by the Movement for the Emancipation of the Niger Delta (MEND) have cut output in the major oil exporter for the last three years.
The dollar weakened against a basket of currencies, offering some support for oil <.DXY>. A Chinese report saying Beijing should increase its holdings of euros and yen in its foreign reserves knocked the U.S. currency.
China was again the bright spot for the global economic outlook, following comments by Vice Premier Li Keqiang that the country's economic recovery has consolidated after having performed better than expected.
Its strong economic growth was reflected in a 12.5 percent year on year jump in implied oil demand, the sixth rise in a row and first double-digit growth since August 2006.
The earnings season continues this week, offering more clues about the strength of economic recovery.
Energy, telecom and consumer goods companies will be in the spotlight with Exxon Mobil
The oil price rally has caused some concern within the Organization of the Petroleum Exporting Countries, prompting some officials to raise the prospect of increasing its oil output.
OPEC will lift supply to protect the global economic recovery at a meeting in December if oil prices rise to $100, Jose Botelho de Vasconcelos, the group's president, said on Sunday.
(Additional reporting by Fayen Wong, Editing by William Hardy)