New York's main contract, light sweet crude for October delivery, slumped 40 cents to $73.69 a barrel.
Brent North Sea crude for delivery in October slipped 45 cents to $77.29.
Poor openings by major Asian bourses were pulling down oil prices, said Victor Shum, senior principal of Purvin and Gertz energy consultants in Singapore.
"I think right now it's really the knock-on effect from equities in Asia.... Oil is pulling back as Asian stocks are coming off," he told AFP.
Japanese, South Korean and Singapore stock markets were down in early Asian trade, with the Nikkei index the hardest-hit, losing 1.38 per cent in the first minutes of trading.
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Traders in Japan were spooked by a surging yen, which hit a 15-year-high against the US dollar yesterday even as the Bank of Japan Tuesday promised to intervene to curb its continued rise if necessary.
The central bank yesterday kept its key interest rate unchanged at 0.1 per cent to continue nurturing a moderate recovery, but pledged "policy actions in a timely and appropriate manner" if needed.
This was in addition to the bank extending a multi-billion dollar loan programme to curtail the strengthening yen last week, which was received poorly by the market as stocks slumped and the yen rose further following the announcement.