By Mark Stevenson
The Associated Press

CIUDAD DEL CARMEN, Mexico — An oil platform leak that has spilled thousands of barrels of crude into the Gulf of Mexico could take several months to repair, state oil monopoly Petroleos Mexicanos said.

Since a drilling rig slammed into a production platform Oct. 23, killing at least 21 workers, a total of 11,700 barrels of oil — about 420 a day — have seeped into the gulf, Pemex Assistant Director for Exploration and Production Pedro Silva Lopez told reporters invited to fly over the site with company and environmental officials.

Pemex previously estimated the spill at nearly 13,000 barrels.

A fire was still raging Wednesday at the damaged well, about 20 miles offshore from the port of Dos Bocas in the Gulf coast state of Tabasco, but only faint traces of crude could be seen shimmering on the water.

The company plans to install a new valve assembly to replace a damaged one on the well, but Silva said officials are not sure that will stop the leak.

If it doesn't, another procedure to block the damaged well could take as long as four to five months to complete, said Carlos Morales, Pemex's director of production and exploration.

Silva said at least two beaches in the Gulf coast states of Tabasco and Campeche have been affected by the oil spill, but the full extent of the damage has not been determined.

The spill is far smaller than a major disaster like the 1989 Exxon Valdez supertanker spill that released about 260,000 barrels, or 11 million gallons of oil into Alaska's Prince William Sound. Each barrel of oil contains 42 gallons.

Pemex is losing about 5,700 barrels of oil a day in production at the offshore platform. The company expects the average daily production this year to finish slightly above 3.1 million barrels, said Jesus Reyes, director-general of Pemex.

The company's daily output in 2006 was 3.26 million barrels, according to the U.S. Energy Information Administration.

Pemex has promised both internal and external investigations of the collision in high seas between the platform and a drilling rig operated by a subcontractor.