New York's main contract, light sweet crude for delivery in October, fell 35 cents to $72.75 a barrel.
London's Brent North Sea crude for October slipped 30 cents to $73.32.
A host of factors appeared to be working against crude prices, said Victor Shum, senior principal of Purvin and Gertz energy consultants in Singapore.
"The shaky global economy continues to put pressure on crude prices and the pullback in the US equities market yesterday has also contributed to oil prices coming down," he said.
The Dow Jones Industrial Average fell 0.38 per cent to 10,174.41 late yesterday.
Japanese shares dropped below the 9,000-point level for the first time since May 2009 shortly after opening today.
Singapore, Hong Kong and South Korean equities markets were also down in early trade.
The euro retreated against the greenback today, with one euro buying $1.2632 compared with $1.2654 late yesterday.
Weak gasoline demand during the US summer driving season, which is due to end in two weeks, also painted a grim picture of oil fundamentals, he added.
"The sentiment in the market is therefore quite bearish, forcing many investors to sell," Shum stated.