American adventurer Steve Fossett is drifting slowly toward Chile as he nears the halfway point of his attempt to fly a balloon around the world alone. Mr. Fossett's mission control team in St. Louis, Missouri, says it is closely monitoring the balloon's oxygen supply and slow winds over the Pacific.

By late Tuesday, Mr. Fossett's Solo Spirit balloon was about 1,100 kilometers off the coast of Chile, 7,600 meters above the Pacific Ocean and moving at a slow 39 kilometers per hour. Chief controller Joe Ritchie says it means a longer trip with oxygen supplies running low.

"The main change has been that these slow winds keep lengthening the expectation of how long you are going to take," he said, "and as that lengthens, the oxygen deficit gets that much greater and it means that much longer you are going to have to fly at low altitudes."

Mr. Ritchie says Mr. Fossett needs to use oxygen when flying above 5,800 meters, and he will have to climb 3,000 higher than that to make it over the Andes mountains this week. Once over the mountains, he will be able to fly low enough to conserve oxygen, but high enough - around 5,800 meters - to avoid weather problems.

Mission meteorologist Bob Rice said "that level is typically above most of the water droplet clouds. I say that for icing considerations. Balloons will ice and they will ice badly."

Earlier Tuesday, Mr. Fossett had to climb onto the roof of his capsule to repair a propane tank hose in temperatures well below zero.

The Solo Spirit control team says the balloon is holding up well and the weather ahead looks good. Controllers say Mr. Fossett should reach the South American coast sometime Wednesday, and that his speed should double once he crosses the Andes. Chief controller Joe Ritchie says he is confident Mr. Fossett can press on toward Australia even if he runs out of oxygen later this week.

"In principle, there is no reason you can not get all the way to Australia," he said, "but this is a balloon. As much as we like to think we are flying there, we are really just drifting there," said Mr. Ritchie.

This is the sixth time the former Chicago stock trader has tried to fly a balloon solo around the world. Two men - Swiss pilot Bertrand Piccard and his British co-pilot Brian Jones - completed the first-ever trip around the world by balloon two years ago.