By Erwin Seba and Bruce Nichols

HOUSTON (Reuters) - An oil and gas platformoperated by Mariner Energy <ME.N> burst into flames on Thursdayand unleashed a mile-long oil sheen into the Gulf of Mexico, inthe region's first major offshore disaster since BP's oil spillbegan in April.

All 13 crew members were rescued with no injuries from theocean near the burning platform and were taken to anotheroffshore platform, the U.S. Coast Guard said. The fire has beencontained but is not yet extinguished.

It is not known whether the oil sheen came from the damagedplatform or the well, which is in relatively shallow water at340 feet (104 meters) deep.

Reuters Insider video on market overreacting to fire

Factbox on U.S. energy disasters [ID:nN02230465]

Graphic on Mariner Energy platform fire:

The platform is located more than 90 miles (145 km) southof Louisiana's Vermilion Bay, west of BP Plc's ruptured Macondo well that killed 11 people and caused theworld's worst offshore oil spill.

At the moment, the accident does not appear to be anotherBP-style disaster, said Raoul LeBlanc, a senior director at PFCEnergy in Houston.

"If it's an industrial accident and doesn't involve a wellit's obviously still bad, and we hope that no one has beenhurt, but it's unlikely to have long-term implications forproduction in the Gulf of Mexico," LeBlanc said.

The platform was undergoing maintenance and was not inactive production, the U.S. Interior Department said. It wasauthorized to produce oil and natural gas.

Material being stored on the platform -- not oil coming upfrom the well -- was causing the blaze, which was nearlyextinguished, Louisiana Governor Bobby Jindal said.

The seven-well platform's output is a small fraction of the1.6 million barrels of oil the region produces on a dailybasis.

The facility averaged 9.2 million cubic feet of natural gasper day and 1,400 barrels of oil and condensate per day duringthe last week of August, Mariner said.

White House spokesman Robert Gibbs said he did not knowwhether the fire would affect the Obama administration'scurrent deepwater drilling moratorium. Environmental groupssaid the explosion showed the need to keep the moratorium inplace.

News of the fire helped push up crude oil prices $1.06, or1.45 percent, to $74.99 a barrel on the New York MercantileExchange. Oil prices were also boosted by Hurricane Earl, whichis threatening refineries along the U.S. East Coast. [O/R]

Shares of Mariner Energy fell 2.4 percent to $22.79 andshares of Apache Corp , which is expected to buy MarinerEnergy, also fell 1.8 percent to $90.82 [ID:nN02219360]

Mariner has participated in at least 35 deepwater projectsin the Gulf and operated over half of them.

Pritchard Capital analyst Stephen Berman said the market over-reacted to the news when it initially pushed Mariner'sshares down 5 percent.

"As more details come in, it's an incident. It'sunfortunate but it sounds like it's under control," he toldReuters Insider.

(Additional reporting by Kristen Hays, Anna Driver andEileen O'Grady in Houston, David Sheppard and Joshua Schneyerin New York, and Tom Doggett and Ayesha Rascoe in Washington;writing by Andy Sullivan; editing by Lisa Shumaker)