Worries about weaker economic growth dragged down oil prices Monday.
Oil has now fallen five of the last six trading days. It fell more than 6 percent last week.
Benchmark crude fell 96 cents, or 1 percent, to finish at $91.93 on the New York Mercantile Exchange. Prices for other petroleum products dropped, too.
In London, Brent crude dropped $1.61 at $109.81 on the ICE Futures exchange.
Germany delivered the latest dose of gloomy economic news, with its Ifo index of business confidence falling for the fifth month in a row. Germany is an economic powerhouse, but 43 percent of its exports go to its euro partners. And growth is stalling across the other 16 countries in the eurozone.
Slower economies mean less demand for oil, pushing prices down.
Phil Flynn, a senior market analyst for Price Futures Group, said he's surprised prices haven't fallen further. He said one reason could be that commodity funds have not been bailing out of oil.
Still, oil prices have been under pressure from worries about Europe. The dollar has been stronger, which makes oil cheaper for holders of other currencies.
"You're seeing demand destruction around the globe," he said. "You've got Saudi Arabia saying they're going to pump oil until the cows come home." All of that drives down oil prices, he said.
The lower oil prices are somewhat positive for drivers in the U.S. The average price for gasoline slipped about 2.5 cents over the weekend to $3.808 per gallon, according to a daily survey from AAA, Wright Express and the Oil Price Information Service.
For other futures prices on the New York Mercantile Exchange:
Natural gas fell 4.8 cents to settle at $2.837 per 1,000 cubic feet.
Heating oil fell 2.2 cents to $3.0987 per gallon.
Wholesale gasoline fell 2.49 cents to $2.9176 per gallon.