New York's main contract, West Texas Intermediate crude for delivery in March, was down 56 cents at $97.28 a barrel in morning trade. Brent North Sea crude for March delivery gained 25 cents to $114.83.
"Oil prices remain affected by strong bullish and bearish factors," said Ken Hasegawa, energy desk manager at Newedge brokerage in Japan.
While concerns over a supply disruption in Africa and Iran remained strong, prices were being weighed down by the dragging talks on Greek sovereign debt, Hasegawa told AFP.
Athens has been in talks with the European Union, the International Monetary Fund and the European Central Bank on further action needed to unlock a new eurozone rescue deal worth 130 billion euros ($171 billion) pending since October, but no agreement has been reached yet.
Pressure is also high for an agreement with private lenders to wipe out part of the 350-billion-euro Greek debt, as Athens faces loan repayments of 14.4 billion euros ($19 billion) on March 20.
Meanwhile, a Nigerian militant group on Sunday said it had destroyed an oil pipeline in the Niger delta -- the home region of President Goodluck Jonathan -- a week before governor's elections were to be held there.
The Movement for the Emancipation of the Niger Delta (MEND) also threatened more attacks in future to "reduce Nigerian oil production to zero and drive off our land thieving oil companies".
Nigeria, which is still reeling from the after-effects of widespread protests in January caused by the government's scrapping of fuel subsidies, has also been under pressure from a series of Islamic militant attacks.
Africa's most populous nation produces more than two million barrels per day and is a key supplier of crude to the United States and European Union.Traders were also closely monitoring the situation in the Middle East, as tensions between Iran and the West remain high, analysts said.
Crude producer Iran, which is already under four rounds of UN sanctions, vehemently denies its nuclear programme masks an atomic weapons drive as the West alleges, and insists that it is for civilian purposes only.