Brent crude oil fell below $30 a barrel for the first time in nearly 12 years on Wednesday as an increase in US crude and fuel inventories added to the global oversupply.
In London, Brent North Sea crude for February, the European benchmark for oil, fell 55 cents to $30.31 a barrel, its lowest level since February 2004 and below the WTI price.
Earlier Brent sank to $29.96, its lowest level since April 2004.
US benchmark West Texas Intermediate (WTI) for delivery in February pared earlier gains to close up a scant four cents at $30.48 a barrel on the New York Mercantile Exchange.
The US government's weekly inventories report Wednesday snapped attempts by the benchmark contracts to rebound.
The report showed a build in US commercial crude-oil stockpiles of 200,000 barrels in the week ending January 8.
More significant was an 8.2 million barrel surge in gasoline inventories, and a 6.1 million barrel surge in distillate stocks, suggesting very sluggish consumption in the country.
The report painted "a very bearish picture" of the market, said Bob Yawger, director of the futures division of Mizuho Securities USA.
"Crude oil numbers... are only 7.6 million (barrels) below their all-time record of 490.1 million," he said.
Yawger also noted that crude-oil storage at the key Cushing hub was at an all-time record and nearing the terminal's maximum capacity, while gasoline's increase by 19 million barrels in the past two weeks was the biggest two-week build in history.
The looming return of Iranian oil exports to the market after Iran meets the conditions of its nuclear deal with major powers hung over sentiment.
The Iranian government predicted Wednesday that the final implementation of Iran's nuclear program deal is expected by Sunday. US and European officials have said it could be just days away.
"There's increased chatter about new Iranian barrels coming to the market very quickly as the IAEA (International Atomic Energy Agency) supposedly is going to verify over the weekend that Iranians have done enough to verify their side of the sanction deals," Yawger said.