Oil inched higher on Tuesday after a power failure that halted exports out of Iraq's Basra terminal reminded traders about the vulnerability of crude production. US light crude settled at $65.71 a barrel, up six cents, after falling as low as $64.65. London Brent crude rose 15 cents to $64.65 a barrel.
Loadings and exports from Iraq's southern Basra oil terminal could return later on Tuesday after the power glitch, a shipping source said.
In Ecuador, which supplies crude mainly to California, protests have cut output. Production remained around two-thirds of its 530,000 barrels per day level after protesters came close to making a deal with the government on Monday.
"Overall, energy prices remain extremely sensitive to any sort of supply disruption," said a report from Refco. "We expect crude to trade a volatile range in the mid-$60s until more demand data become available."
Oil hit a peak earlier this month of $67.10 per barrel.
This week's supply crimps reminded dealers that Iran, the world's fourth largest oil producer, could be a flashpoint after talks broke down between Europe and Tehran over its atomic work. Iran risks United Nations sanctions if it presses on with its nuclear program.
The looming end of the peak driving season in the United States after the September 5 Labour Day holiday and worries that oil prices could eat into economic growth kept a lid on gains.
Comfortable crude stock levels in the United States, the world's largest oil consumer, also limited prices.
Leading global exporter Saudi Arabia said it was concerned by the recent rally but blamed high prices on refinery constraints.
"We are preoccupied by the quick rise in crude prices ... because the problem is not supply on the market," Foreign Minister Prince Saud al-Faisal said. "There is crude on the market but there are structural problems in demand, and if they are not resolved the crisis will continue."
Oil traders remained on the lookout for further trouble.
Tropical Storm Jose, the 10th named storm of an unusually heavy Atlantic hurricane season, hit Mexico and was downgraded into a depression, but not before reviving worries that the peak September storm period is yet to come and could cause further output disruption in the Gulf of Mexico.
With some crude production in the UK North Sea and India already offline, dealers worry that Opec - already pumping nearly flat out - will strain to make up any unexpected outages.
Fears over global supply security and refining constraints have helped keep US oil at an average $53.79 this year versus $41.47 in 2004.
Opec member Nigeria said any talk of raising cartel quotas at a September 19 policy meeting would be "academic" for now as producers are being encouraged to pump at full capacity.
"We are so far from worrying about quotas," Edmund Daukoru, minister of state for petroleum told reporters on Tuesday. "I think for now Opec will be happy for any member who has the capacity to produce."