month swaps for benchmark Dubai jumped, trading at a premium to the second-month contract for the first time since June, in a market structure that denotes tighter supplies and is known as backwardation. September Dubai climbed to a premium of 4 cents a barrel to October swaps, up from a discount of 16 cents Tuesday, while October jumped to a premium of 5 cents to November, up from a discount of 10 cents, Reuters data showed. Traders were left speculating about the reason for the sudden jump, as no information had emerged about any production outages in the Middle East. The US sold about 30 million barrels of light sweet crude from its Strategic Petroleum Reserve in the past two months as part of the collective release of emergency stockpile coordinated by the International Energy Agency. World oil prices climbed Wednesday ahead of the latest weekly snapshot of energy inventories in the US and one day after sliding on fears of weaker demand. Traders shrugged off a eurozone meeting that failed to land a killer blow in the battle to restore debt confidence. New York's main contract, West Texas Intermediate light sweet crude for September delivery, gained 97 cents to $87.62 a barrel. Brent North Sea crude for October delivery jumped by $1.14 to $110.27 a barrel. The September contract expired at the close on Tuesday. "The mood is still nervous on the crude oil market, with all news causing the market to react markedly ... in its search for some direction," said Commerzbank analyst Carsten Fritsch. Market expectations are for American crude reserves to have fallen by 600,000 barrels in the week to August 12, according to analysts polled by Dow Jones Newswires. Gasoline or petrol inventories are forecast to drop 1.2 million barrels, while distillates -which include diesel and heating fuel - are seen rising by 500,000 barrels. Attractive arbitrage economics are also encouraging shipments of Oman crude to the US west coast, traders said, clearing a surplus that had been expected to weigh on prices of October cargoes. Finally, some traders speculated such a sharp increase in Dubai and Oman values could be related to an unplanned production shutdown. "Because of the big surge in Oman values, the only reason should be a very big reason, some supply shortage from the Arabian Gulf," a trader said. October Oman traded on the DME jumped 91 cents to a premium of $1.03 to Dubai swap quotes at 0830 GMT, using the settlement price for DME futures, the ICE one-minute marker for Singapore and the Brent
