SemGroup, the US physical oil trader, yesterday filed for bankruptcy as it acknowledged losses of more than $3.2bn in different energy markets after betting this year that crude oil prices would fall. Its collapse came as oil prices plunged to their lowest levels since early June. West Texas Intermediate crude oil fell to an intraday low of $125.63 a barrel, down $5 on the day.

Traders sold oil futures as news emerged that tropical storm Dolly was set to miss oil and natural gas installations in the US Gulf of Mexico. Signs of slower oil demand in the US during the summer season also contributed to the sell-off, analysts said. Nauman Barakat, of Macquarie in New York, said: "Overall my bias remains to the downside and I still would like to sell rallies rather than buy dips."