Crude prices slid on Thursday, mirroring other financial markets, amid investor unease over the fast-moving eurozone debt crisis.
New York's main contract, West Texas Intermediate (WTI) light, sweet crude for delivery in September, fell 98 cents to $97.42 a barrel.
Brent North Sea crude for September delivery dropped $1.16 to $116.99 in London trade.
"Crude oil futures remained in the recent range... with uncertainty still regarding the imminent release of details from a summit meeting on Greek debt plans," said Brenda Sullivan, an analyst at Sucden Financial.
German Chancellor Angela Merkel voiced optimism that eurozone leaders will reach a deal to settle Greece's debt crisis and stop it spreading at a crucial summit on Thursday.
"I think we will be able to decide on a new programme for Greece" that will "attack the root of the problems," she told reporters, referring to the emergency aid Greece needs to avert a disastrous debt default.
Merkel and her fellow eurozone leaders were gathering to agree on a way of easing Greece's massive debts. Analysts warned it could be the last chance to avert market panic throughout the eurozone.
Oil prices had risen on Wednesday as news of declining US crude inventories signalled strengthening energy demand in the world's largest economy.
Crude oil inventories in the United States fell 3.7 million barrels in the week ending July 15, according to a weekly report from the US Department of Energy.
The decline was steeper than market expectations for a drop of 1.4 million barrels.
Oil markets also advanced on optimism that politicians in Washington would reach a deal to raise the US federal government's debt ceiling and avert a potentially catastrophic default, analysts said.