The contract fell $1.01 to close at $109.52 a barrel on the Nymex on Monday.
Oil prices have risen sharply in recent days following President Barack Obama's call for military action against the government of Syrian President Bashar Assad in retaliation for what the White House says was a chemical weapons attack against civilians.
But on Monday, there was reason to hope for a diplomatic solution when Syria's foreign minister welcomed a suggestion to move all the country's chemical weapons under international control.
Analysts said it could also hurt Obama's attempts at gaining congressional support for military intervention.
"Backed by the U.N., Russia is arranging for Syria to turn over its chemical weapons to avert a confrontation," said Vishnu Varathan of Mizuho Bank Ltd. in Singapore.
"By deflecting the approaching strike, Russia has also created greater uncertainty in the U.S. Congress on the vote over Syria though the U.S. is still leaning towards a strike." Obama plans to address the nation from the White House on Tuesday about Syria.
Brent, the benchmark for international crudes, dropped $1.03 to $112.69 per barrel on the ICE Futures exchange in London.
In other energy futures trading on Nymex:
- Wholesale gasoline fell 2.8 cents to $2.774 per gallon.- Natural gas rose 1 cent to $3.614 per 1,000 cubic feet.- Heating oil retreated 1.8 cents to $3.0999 per gallon.