Hurricanes Katrina and Rita destroyed 109 oil platforms and five drilling rigs in the Gulf of Mexico, but only a small portion of production will be lost for good, the US government said Tuesday. Rita accounted for most of the damage in a region that ordinarily produces nearly one-third of US crude oil imports, Interior Secretary Gale Norton said in presenting a preliminary assessment report. Rita destroyed 63 platforms and one drilling rig when it tore through the region on September 24, she said. Katrina destroyed 46 platforms and four drilling rigs when it hit the Gulf at the end of August. Katrina also caused extensive damage to another 20 platforms and nine drilling rigs. Rita seriously damaged 30 platforms and 10 drilling rigs. "The two hurricanes coming so close together really illustrate how much of our offshore production was affected," Norton told the CNBC network. "We had altogether, with both of the hurricanes, about 2,900 platforms that were in the path of the hurricanes," she said. "We have no official estimate of the dollar value of the damage and the amount that it will cost to repair those facilities, but it will clearly be in the billions of dollars." In advance of the hurricanes, crude oil production ground to a halt as Gulf sites were evacuated. A total of 342 platforms remain evacuated, roughly 40 percent of the manned sites in the Gulf, Norton said. As a result, 90 pct of crude production and 72 pct of natural gas output is paralysed, she said. But Norton also stressed that only one of the damaged platforms was built after federal construction standards were tightened in 1988. The ones that were destroyed were nearing the end of their lives. "As a result, only a very small percentage of production is expected to be permanently lost," she said in a statement. "Despite such intense winds and powerful waves offshore, we experienced no loss of life or significant spills from any offshore well on the outer continental shelf," Norton added.