On the New York Mercantile Exchange, a barrel of WTI light sweet crude for June delivery slipped to $112.28, down one penny from Thursday's closing level.
Financial markets on both sides of the Atlantic were closed in observance of Good Friday, and major European markets remained closed on Easter Monday.
Shortly after NYMEX trading began Monday, the benchmark West Texas Intermediate futures contract hit $113.48 a barrel, a fresh high since September 2008.
But buying lost momentum in "a natural unwinding of the risk premium that had been built before the long weekend," said Matt Smith of Summit Energy.
Investors continued to worry about political unrest in the Middle East and North Africa, where the "problems are just not going away, in fact they're getting worse if anything," Smith said.
In oil-producing Libya, NATO bombs wrecked Libyan leader Moamer Kadhafi's office in his immense Tripoli residence on Monday, while rebels in besieged Misrata said they had pushed loyalist forces out of the city.
"The Libyan rebels announced they would not be able to export any crude oil for another four weeks due to damages to some of the pumping stations" in the field they control, said Andy Lipow at Lipow Oil Associates.
Lipow also pointed to unrest in oil-exporting Yemen, citing "the potential for export disruption out of that country."
Security forces and loyalists of Yemen's President Ali Abdullah Saleh shot dead two protesters on Monday as hundreds of thousands turned out to demand his immediate ouster, medics and witnesses said.
Anti-Saleh protests, in which more than 130 people have been killed since January, have led to defections and clashes within the army. But the Republican Guard has remained loyal.
The latest violence came as the United States urged a peaceful transition after Saleh's ruling General People's Congress said on Saturday it accepted the Gulf Cooperation Council's transition plan under which Saleh would quit in 30 days with immunity from prosecution.
The protesters, who have been demonstrating across Yemen since late January, rallied against the GCC plan. "No rest, no respite for the executioner," they shouted.