New York's benchmark light sweet crude July contract leapt 1.15 dollars to 30.71 dollars a barrel.

In London, the price of benchmark Brent North Sea crude oil for July delivery climbed 1.08 dollars to 27.40 dollars.

"There is just a good deal of uncertainty with Iraq production and questions about the actual output of Venezuela," said Fimat USA analyst John Kilduff.

"It puts the market higher, with supplies that are tight," he said. "The market is going to stay vulnerable until we start seeing the Iraq oil in the inventories."

Kilduff predicted that the Organization of Petroleum Exporting Countries (OPEC) would hold quotas steady while urging members to show more respect for the ceilings.

In London, GNI trader Robert Laughlin said there were concerns about low US gasoline (petrol) stocks as Americans prepared to take to the road for summer vacations.

The market also was nervous ahead of the meeting of the Organisation of Petroleum Exporting Countries (OPEC) in Qatar on June 11 to discuss cutting output, he said.

"With prices as high as they are, OPEC may be more reluctant to decrease quotas," he said.

"There have been general expectations of a cut, and in many respects people are still saying that with Iraq coming on stream OPEC may have to do something. But there seems to be no reason to do so at the moment."

OPEC's dilemma is that it is still unclear how long it will take for Iraqi production to recover now that sanctions have been lifted on the country.

Iraq's oilfields were seized almost intact, and their output climbed from near zero at the end of the war to around 800,000 barrels per day (bpd) as of last week, according to Iraqi officials.

Total current output exceeds the amount needed for domestic consumption by about 200,000 bpd, still a fairly small amount by global standards.

Crude pumping at the export terminals, the offshore Mina al-Bakr facility in the Gulf and Ceyhan on the Turkish coast, meanwhile has been hampered by logistical difficulties.

"The Iraqi situation is a big problem," said Commerzbank analyst Jon Rigby in London.

"Iraq being out makes the OPEC meeting more difficult. It would be better if we knew exactly where Iraq stood, even if it had started exporting as OPEC would have a background on which to make a decision."