US oil prices struck new highs above $42 a barrel on Wednesday amid worries that sabotage against oil infrastructure in Saudi Arabia could destabilise the world's biggest crude exporter.
The latest rally to 21-year peaks has raised doubts about whether an increase in supplies from the Opec producers' cartel will be enough to tame prices when ministers meet on Thursday
US light crude hit $42.45 a barrel, the highest since futures were launched in New York in 1983.
The US crude was 13 cents down at $42.20 a barrel, while London's benchmark Brent crude slipped 38 cents to $38.70 a barrel.
Traders were already nervous that escalating violence in the vital Middle East might lead to sabotage on oil infrastructure in the region, which pumps more than a quarter of world supplies.
Militants attacked a Saudi petrochemical compound earlier in May, and there have been strikes against the key Basra oil export terminal in Iraq.
Now oil traders fear the latest incident could be the start of a concerted al Qaeda offensive to disrupt Saudi supplies at a time when oil prices are already high enough to threaten world economic growth.
Analysts estimate a risk premium of between $5 and $9 has been factored into the price of a barrel of oil due to the possibility of an attack on a major oil installation.
Neighbouring Kuwait said it was stepping up security at its oil installations and was coordinating with fellow Gulf producers - Saudi Arabia, the United Arab Emirates and Qatar - to protect against attacks.
Riyadh has vowed to keep supplies running smoothly from its heavily guarded oil facilities. It is the only Opec producer with significant spare capacity. It has already raised output to 9.1 million barrels a day (bpd) in an effort to dampen prices, and it has called on Opec to lift supply limits by 2-2.5 million bpd.
The group is already pumping about two million bpd above its existing official ceiling of 23.5 million bpd, and some producers arriving in Beirut conceded there was little they could do to quell the surge in prices.