A giant tanker refitted to scoop up spilled oil is being tested at the site of the Gulf of Mexico oil leak.
The Taiwanese vessel - called "A Whale" - is designed to vacuum up oily water, separate the oil and return the water to the sea.
It is undergoing two days of testing before starting work, a Coast Guard spokeswoman said.
Much smaller skimming vessels have been working off Louisiana, but they have been affected by rough seas.
"We are skimming today in Louisiana, but not in Alabama, Mississippi and Florida," Coast Guard spokeswoman Stephanie Hebert told the AFP news agency.
Oil has been gushing from a ruptured well in the Gulf of Mexico since 22 April, when BP's Deepwater Horizon rig exploded and sank.
Crude oil has been leaking at a rate of between 35,000 to 60,000 barrels per day, according to US scientists.
Two containment ships capturing about 25,000 barrels of oil per day are now in place, and there are plans to double this by connecting a new vessel, the Helix Producer.
But these plans have been delayed by tropical storm Alex, which brought high seas and strong winds to the region.
Offshore skimming in Alabama, Mississippi and Florida has been on hold for almost a week.
Testing of the giant skimmer vessel - which its owners say can process 21 million gallons of oily water per day - began on Saturday.
The 275m (300-yard) tanker takes in oily water through 12 vents.
In a series of tanks, the oil is separated for transfer to another vessel, while the clean water is returned to the sea.
"In many ways, the ship collects water like an actual whale and pumps internally like a human heart," Bob Grantham, a spokesman for TMT Shipping, told the Associated Press news agency.
"A Whale" is currently operating north of the wellhead area and results from the testing are expected on Monday.
If successful, the vessel could provide a boost to clean-up efforts.
Admiral Thad Allen, who is overseeing the response to the spill, also said that he hoped to have the Helix Producer containment vessel in place by Wednesday, AFP news agency reported.