Oil is leaking at the rate of 1,000 barrels a day after a rig exploded and sank off the coast of Louisiana last week.
The drilling rig, run by British giant BP, went up in flames on April 21 and there are fears the spill will damage beaches, barrier islands and wetlands across the coastline.
It currently covers an area of 1,500 square kilometres.
More than 100 workers were rescued from the rig. 11 of their colleagues are still missing and presumed to have been killed in the accident.
No cause has been established for the blast.
The clean up operation has restarted with submarine robots being used to detect and plug leaks in the rig, known as Deep Water Horizon.