OPEC took no action to ease a global oil-supply glut, resisting calls from Venezuela that the group needs to stem the rout in prices. Futures slumped the most in more than three years.
The group maintained its collective production ceiling of 30 million barrels a day, Ali Ibrahim Naimi, Saudi Arabia's oil minister, said Thursday after representatives of the 12-nation cartel met in Vienna.
Brent crude dropped as much as 8.4% in London after the decision, extending this year's drop to 35%.
Oil has tumbled into a bear market this year as the U.S. pumped its largest amount in more than three decades and conflict in the Middle East and Ukraine failed to disrupt supply.
The Organization of the Petroleum Exporting Countries has kept its 30-million-barrel limit in place since 2012, but the group actually has been producing more -- almost 1 million barrels more last month, data compiled by Bloomberg show.
"OPEC has chosen to abdicate its role as a swing producer, leaving it to the market to decide what the oil price should be," said Harry Tchilinguirian, head of commodity markets at BNP Paribas in London. "It wouldn't be surprising if Brent starts testing $70."
Brent, a global benchmark, is poised for its biggest annual decline since 2008. Futures fell the most since May 2011 and traded down $4.81 to $72.94 a barrel on Thursday in London.
Brent but also influences U.S. oil and gasoline prices. In electronic trading -- U.S. commodities and stock markets were closed Thursday -- West Texas Intermediate crude dropped as much as $5.94 to $67.75 a barrel, its lowest level since May 25, 2010. Prices have decreased 30% this year.
"The change is that it's no longer Saudi Arabia and OPEC that are going to be managing the supply side of the market," said Michael Wittner, head of oil market research at Societe Generale. "That is so fundamental, it is hard to overstate."
OPEC will meet again on June 5, according to a delegate, who asked not to be identified in line with policy.
"We are not sending any signals to anybody, we just try to have a fair price," OPEC Secretary-General Abdallah Badri said at a news conference after the meeting. The group will abide by the limit, he said.
Iranian Oil Minister Bijan Namdar Zanganeh told reporters after the meeting that he was "not angry" about the decision but that it was "not in line with what we wanted."
Venezuela, whose currency reserves are close to their lowest level in 11 years, planned to push for a production cut, Rafael Ramirez, the country's OPEC representative, said before the meeting started.
"Everybody has to make some sacrifice," Ramirez said, estimating the global oversupply at 2 million barrels a day. Kuwait put the glut at 1.8 million barrels.
Ministers from Kuwait, the United Arab Emirates and Angola also said they were concerned about the surplus in the market as they arrived at the group's headquarters.
West Texas Intermediate, the U.S. benchmark, dropped as much as 8.1%, extending this year's slump to 30%. Futures declined $4.69 to $69 a barrel on the New York Mercantile Exchange.