Uncertainties about supply from Iraq, while always present, typically focus on the repeated attacks on the northern Kirkuk-Ceyhan export pipeline - still operating only sporadically. However, it was the southern infrastructure that was shut down in late August, as an assault on the electricity network resulted in a blackout and a halt to exports from the Basra and Khor al-Zubair terminals. Sales partially resumed on 23 August.

Worries about the increasingly narrow supply cushion were highlighted by the sharp market reaction to two relatively minor disruptions. Both were caused by public protests, one in the habitual hotbed of Nigeria, the other in Ecuador. And after a brief lull, predictions of serious storms in the Atlantic are returning, with Tropical Storm Katrina now on the horizon. 'The potential course and intensity of Katrina would have no long-term impact, but in terms of whether the move is towards $60 or $70 [a barrel], it is of some significance,' says Paul Horsnell of Barclays Capital.

The impact of sustained high oil prices on the global economy is set to be highlighted by the IMF imminently, when it releases its annual World Economic Outlook. Initial indications are that the report will warn of oil's increasing risk to global economic growth.