$91 on Wednesday over concerns about an economic slowdown in Europe, China and the U.S.
By early afternoon in Europe, benchmark oil was down 72 cents to $91.17 a barrel in electronic trading on the New York Mercantile Exchange. The contract dropped 59 cents to end at $91.89 per barrel in New York on Tuesday.
Brent crude, which is used to price international varieties of oil, was down 95 cents to $110.62 a barrel on the ICE Futures exchange in London.
Investors remain concerned about Europe's ongoing financial crisis after Spain's prime minister said a request for bailout funding isn't imminent.
"The oil market has been under pressure for a fourth consecutive day ... amid persistent concerns about a global economic slowdown that currently limits risk appetite," said a report from Sucden Financial in London.
Slower growth in China, which is a huge importer of oil, has also kept a lid on oil prices. Slower growth can cut demand for oil and other energy products.
Worries have meanwhile intensified that the U.S. economy will fall off a "fiscal cliff" at the end of the year. That's when tax increases and deep spending cuts will take effect unless Congress reaches a budget deal. A recession could follow.
"There is downside risk in the overall market," said Ric Spooner, chief market analyst at CMC Markets in Sydney. "Oil is one of those commodities where I think demand is well-covered by current supply capacity."
In other Nymex energy futures trading:
— Natural gas lost 6.6 cents to $3.465 per 1,000 cubic feet. It ended at $3.531 Tuesday, a high for the year. That price was 85 percent above the low for the year of $1.91 reached in April.
— Heating oil was down 1.28 cents at $3.1127 a gallon.
— Wholesale gasoline dropped 4.11 cents to $2.8281 per gallon.
Pamela Sampson in Bangkok contributed to this report.