Oil prices had the biggest one-day gain on record overnight as a new storm beared down on America's southeast coast, threatening more supply disruptions less than a month after Hurricane Katrina.

Hurricane Rita grew in strength today as it passed over the warm waters off Florida. It is forecast to push into the Gulf of Mexico, where the United States produces a quarter of its oil.

By Sunday, the storm could make landfall in Texas, home to about a quarter of the nation’s refining production.

Organization of Petroleum Exporting Countries, in an effort to reassure markets edgy over supplies, agreed today to make available 2 million extra barrels of oil a day if needed.

Opec confirmed it the will offer the extra oil for three months starting October 1st. The cartel's production ceiling remains unchanged at 28 million barrels a day.

Analysts believe the promise of extra supplies will have little effect on prices, given the shortage is of refining capacity rather than raw product.

"Opec ministers are keen to at least symbolically take some pressure off markets," analysts at UBS argued. "Actual production is unlikely to rise by much, however, as spare capacity is limited and few customers want more crude oil."

New York’s main crude contract for October delivery, which expires later today, eased 69 cents to $66.70 per barrel during electronic trading this morning. The futures yesterday surged by 7 per cent on concern that Rita could follow a similar path to Katrina, which devastated production and refining facilities in the Gulf.

Meteorologists say there is about a 40 per cent probability Rita will disrupt production in the Gulf. The storm is still too far away to forecast with greater certainty.

Four of the region's coastal refineries and about half its oil production remain out of service following Katrina, meaning the industry can ill-afford more stoppages.

Oil futures reached a record high of $70.85 on August 30, then eased as Washington and other major economies tapped some of their emergency reserves.

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