US oil prices tumbled below $60 a barrel for the first time since July 2009 on Thursday, taking the shocking loss since June to about 44 percent.
Prices held up for most of the day before sinking more than $1.00 in the final two hours of trade on the New York Mercantile Exchange.
At the close, West Texas Intermediate crude for January delivery, the US benchmark, had lost 99 cents from Wednesday to $59.95 a barrel.
In London, Brent crude for January tracked the same pattern, finishing down 56 cents to $63.68 a barrel.
"Below $60, we're crossing another line here," said James Williams, energy analyst at WTRG Economics of the WTI price.
He said that Wednesday's US stockpiles report, with a rise in levels of stored crude and refined products, just added to the selling pressure on the oversupplied global market.
"There's plenty of supply, more than plenty," he said. "Refineries are running full output, products increasing, and still an increase in crude."
"Conceivably, we could see crude going below $50 for a short period of time," he warned.
"The oil market may be oversold from a technical perspective, but it continues to lack fundamental support for a meaningful reversal to the upside," said Tim Evans of Citi Futures.