Oil prices fell Thursday after the European Central Bank announced no immediate action on the eurozone sovereign debt crisis, disappointing investors.
New York's main contract, light sweet crude for September, finished at $87.13 a barrel, down $1.78 from Wednesday's closing level.
Brent North Sea crude for delivery in September slipped six cents to $105.90 a barrel in London trade.
ECB president Mario Draghi, after a one-day monetary policy meeting Thursday, revealed no concrete measures to ease debt pressures in the eurozone.
Europe's main stock exchanges retreated as traders were disappointed that encouraging comments by the central banker last week were not backed up by new policy steps.
"It seems that Mario Draghi's speech was fairly bewildering, creating more uncertainty about the fragile economic conditions in the eurozone and hurting investors' sentiment," said Sucden brokers commodities analyst Myrto Sokou.
"Thus, the euro came under pressure against the US dollar, prompting investors to another round of sell-off in the markets."
A stronger US currency makes dollar-priced crude oil less attractive to buyers using weaker currencies, tending to dent demand.
Oil prices had risen on Wednesday, boosted by a sharper-than-expected drop in US crude stockpiles that sparked hopes for stronger demand in the biggest oil-consuming country.
The US Federal Reserve's decision Wednesday to keep monetary policy unchanged after a two-day meeting was widely expected but disappointed some investors who had hoped for additional economic stimulus.