Hurricane Rita has caused more damage to oil rigs than any other storm in history and will force companies to delay drilling for oil in the US and as far away as the Middle East, initial damage assessments show.

Oil prices eased on Wednesday over concerns that demand for crude would be hit by the continued shutdown of refineries. US crude fell 27 cents to $64.80 a barrel by 06:444 GMT after losing 75 cents on Tuesday.

ODS-Petrodata, which provides market intelligence to the offshore oil and natural gas industry, said it expected a shortage of rigs in the US Gulf this year.

"Based on what we have right now, it appears that drilling contractors and rig owners took a big hit from Rita," said Tom Marsh of ODS-Petrodata. "The path Katrina took was through the mature areas of the US Gulf where there are mainly oil [production] platforms. Rita came to the west where there is a lot of [exploratory] rig activity."

Ken Sill of Credit Suisse First Boston said: "Early reports indicate numerous rigs are missing, destroyed or have suffered serious damage and several companies have yet to report. Rita may set an all-time record."

The US Coast Guard said nine semisubmersible rigs had broken free from their moorings and were adrift.

This damage could not have come at a worse time for oil companies and consumers. US crude futures on Monday fell 37 cents to $65.45 a barrel in midday trading in New York as refineries that were evacuated before the onset of Rita returned to operation.

Earlier in the day, Ali Naimi, Saudi Arabia's oil minister, said the market had not taken up the 2m barrels a day of spare capacity the Organisation of the Petroleum Exporting Countries offered last week. Speaking in Johannesburg, he blamed high oil prices on a lack of industry infrastructure, including rigs and refineries, rather than oil reserves. Rigs, which are movable and are used for exploration and development, were in short supply before hurricanes Katrina and Rita blew through the US Gulf in late August and September.

High oil prices and the desperate search for new oil supplies needed to meet rampant demand from the US and

China have made rigs difficult to find and expensive to hire. Rigs cost $90m-$550m to construct, depending on how sophisticated the structure and how deep the water in which it will drill. A rig ordered today is unlikely to be ready before 2008 or 2009, analysts said.

As a sign of just how precious rigs are becoming to the market, Anadarko, the biggest US independent oil company, this week set a record by committing to a rig six years in advance; commitments in the past were made months ahead of time rather than years.

Initial reports from companies are ominous. Global Santa Fe reported it could not find two of its rigs. Rowan

Companies reported four rigs damaged, with two having moved, one losing its "legs" and the fourth presumed sunk. Noble has four rigs adrift, with two run aground one into a ChevronTexaco platform.