New York's main contract, light sweet crude for October delivery slid 84 cents to 68.45 dollars per barrel.

Brent North Sea crude for October delivery dipped 64 cents to 67.05 dollars in morning London trade.

"The fall is really related to some weakness in equities markets," said Victor Shum, senior principal at energy consultancy Purvin and Gertz in Singapore.

Japanese share prices tumbled 2.32 percent on Monday as investors fretted about pre-weekend losses on Wall Street and a stronger yen, leading to a fall in Asian equities.

Europe's main stock markets also dived in morning trading, erasing more than one percent in Frankfurt, London and Paris.

"We continue to have this tug-of-war between weak supply fundamentals and optimistic hopes of economic recovery, so we are likely to stay in this 65 dollar to 75 dollar range," Shum added.

Before the weekend, oil had slumped on Friday as traders banked profits from a four-day rally spurred by growing optimism that the global economy was emerging from recession.

Last week, the Organization of the Petroleum Exporting Countries (OPEC) decided to maintain its production levels as the cartel, which pumps about 40 percent of the global supply, deemed the market to be "oversupplied".

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