Offshore oil and natural gas platforms in the Gulf of Mexico need to be built as much as 10 feet higher than had been thought, an engineer told the National Hurricane Conference on Thursday.

Research prompted by hurricanes in 2004 and 2005 indicates that new platforms should have decks as high as 50 to 60 feet above the surface — 5 to 10 feet higher than current standards call for, said Frank J. Puskar, president of Houston-based Energy Engineering Inc.

“This is a big, big change for our industry,” Puskar said at a session about hurricanes and offshore petroleum.

Hurricanes Katrina and Rita in August and September 2005 destroyed 113 production platforms in the Gulf of Mexico. A year earlier, Hurricane Ivan had piled up waves 20 feet higher than was then expected for a “hundred-year” storm — as much as 92 feet from their underwater origins to the top, Puskar said.

He said the highest waves are in deep waters, but about half their height is below the surface.

Puskar said the American Petroleum Institute will be coming out with new offshore engineering standards before June, when the 2007 hurricane season starts. Those standards probably will also take into account new findings that waves are much bigger in some parts of the Gulf of Mexico than others, posing greater risks for offshore platforms, Puskar said.

Hurricane Opal made hurricane researchers aware that the storms can intensify suddenly as they cross a deep warm-water eddy called a loop current.

“When Opal came through, we really didn’t notice it because in 1995 we weren’t really working in that area,” Puskar said.

Further, the new research, a joint project of API and the federal Minerals Management Service, found that the loop current also has a significant effect on wave height, he said.

The API proposals would divide the Gulf into four areas. Puskar said the highest waves are likely in a region that runs roughly from waters south of New Orleans to south of a point between Pensacola and Tallahassee, Fla. Both Ivan and Katrina swept through that part of the Gulf.

The vast majority of offshore rigs in the Gulf of Mexico are south of the rest of Louisiana, where the “project waves” are significantly lower, he said. Rita went through that area.

The destroyed platforms made up almost 3 percent of the total in the Gulf of Mexico. However, most were older and in nearly played-out fields, so total production was cut about 1 to 2 percent, said Puskar and Scott Powell, vice president for marine services of Wild Well Control Inc. of Houston.

Another study, to be presented at the Offshore Technology Conference in Houston from April 30-May 3 but already available on Energo’s Web site, found that 62 of the 123 platforms destroyed by Ivan, Katrina and Rita had been built before 1970, and another 37 before 1990.

Even some newer platforms suffered spectacular damage. Puskar showed a photograph of a tension-leg platform built in 2001 and destroyed by Rita. “It broke its mooring and flipped over,” he said.

Some companies have raised existing platforms to meet new standards in the past, but that is expensive and difficult.

“Most people are just trying to deal with it by taking equipment and things off the lower decks, so they don’t get as easily damaged,” Puskar said.

“Again, those are the biggest waves expected. In the life of a structure, you’re probably not going to see a hundred-year storm. We’re designing for the worst case.”