Ahead of weekly U.S. petroleum inventory reports, U.S. crude stockpiles were forecast to have fallen by 700,000 barrels last week, also supportive for oil futures.
But persistent worries about the euro zone debt crisis and fading hopes that a summit of European Union leaders this week will find a lasting solution to the region's troubles kept price gains limited.
"Brent crude is up due to the ongoing strike by Norwegian oil workers that has shut some production," said Gene McGillian, analyst at Tradition Energy in Stamford, Connecticut.
In London, Brent crude for August delivery was up 50 cents at $91.51 a barrel by 11:23 a.m. EDT (1523 GMT), after surging to a session high of $92.44.
U.S. August crude was down 52 cents at $78.69 a barrel. It shot up earlier to $79.68 on expectations of a stock draw ahead of the weekly inventory data, but retreated, tracking Wall Street, where gains were trimmed on euro zone worries.
Brent's premium against U.S. crude climbed as high as $13.03, shooting up from Monday's $10.73 low, as potential tightness in North Sea supplies began to be factored in, analysts said.
In early trade, rising tensions between Syria and Turkey helped lift oil futures. NATO member states condemned Syria for its shooting down of a Turkish military jet last week and Ankara warned Damascus against any further military moves.
In Norway, the world's eighth-biggest oil exporter, Statoil said it was shutting four oil platforms in the North Sea due to the strike that began on Sunday.
The strike had initially shut down the Oseberg Field Centre consisting of a processing facility and a drilling facility. So far, the action has cut Norway's oil production by 150,000 barrels per day and natural gas output by 4 per cent.
Norwegian trade unions said they would decide on Friday whether to escalate the strike that has involved 700 offshore workers over a pension issue.
Copyright @Thomson Reuters 2012