The fear is underlined by the uncertainty of the United States' presence in Iraq as a continued military or political influence by the Americans could make Iraq and Saudi Arabia, holders of the world's two biggest oil reserves, a target for further attacks. Despite the fact that oil installations were unharmed and indeed, not even the focus of the attack, any concentrated terrorist focus on the region could be destabilising.

Prior to the US invasion, oil prices peaked at a 12 year high of $US40 per barrel over fears of widespread Middle East unrest, but as no significant supply disruptions followed, prices eased to a five month low of $US25 a barrel in late April.

OPEC has sounded its alarm about the volatility of the prices, raising expectations of quota cuts for member nations at the consortium's June 11 meeting. OPEC president Abdullah al-Attiyah said last week the group needed a fresh cut in output to boost prices.