New York's main contract, light sweet crude for delivery in October, was down 71 cents to USD 89.50 a barrel in morning trade, and Brent North Sea crude for October settlement eased nine cents to USD 111.80.
"With the Greek risk overhanging the market, prices have been very edgy, very jumpy," said Nick Trevethan, senior commodities strategist at ANZ Research in Singapore.
On Tuesday, Germany, France and Greece agreed to hold a fresh round of talks on the crisis after US President Barack Obama urged Europeans to greater efforts to calm volatile markets.
German Chancellor Angela Merkel, French President Nicolas Sarkozy and Greek Prime Minister George Papandreou would hold a teleconference today regarding Athens's debt emergency.
Merkel had earlier sought to soothe traders' fears over Greece, stressing that everything would be done to avoid an "uncontrolled insolvency" and emphasising the eurozone would remain intact.
Efforts to increase crude production by Libya following the ouster of veteran leader Muammar Gaddafi remain under threat after forces loyal to the fallen dictator attacked oil infrastructure on Monday, analysts said.
The International Energy Agency yesterday revised its expectations of Libyan crude production capacity from zero to between 350,000 and 400,000 barrels per day by the end of 2011, rising to 1.1 mbd by the fourth quarter of 2012.
"However, if the attack by pro-Gaddafi forces on oil infrastructure on Monday marked a shift in tactics, it will put the Libyan production at risk," Trevethan said.
Gaddafi, wanted for alleged crimes against humanity by the International Criminal Court, remains in hiding but many of his inner circle and one of his sons have fled to neighbouring Niger.