New York's main contract, West Texas Intermediate light sweet crude for November delivery, was down 23 cents to $80.28 in afternoon trade, extending a massive 6.3 percent, or more than five-dollar, fall in the US session Thursday.
The contract had rebounded in early trade on bargain-hunting but economic fears quickly overpowered positive sentiment, analysts said.
Brent North Sea crude for November settlement was up 46 cents to $105.95, but the gains were narrower. The contract plunged $4.87 overnight.
The continued market weakness "reflects the waning ability of monetary policymakers (in the United States) to convince investors they can right the economy," research house Capital Economics said.
"We doubt this will change, even if bolder stimulus is undertaken in due course," it said in a commentary.
"The bottom line is that the stock market and commodities are likely to continue to struggle given the gloomy outlook for the economy that the Fed openly acknowledged on Wednesday."
The US Federal Reserve warned on Wednesday about significant downside risks to the world's biggest economy, which has yet to fully recover from a recession in 2009, the country's worst since the Great Depression in the 1930s.
