Tests of a giant tanker refitted to scoop up oil spilled in the Gulf of Mexico have been inconclusive because of high seas, operators said.
The tests were supposed to be completed on Monday.
But Bob Grantham, spokesman of ship owner, TMT Shipping Offshore, said that there would now be an additional testing period.
If it works, the so-called "super skimmer" could boost efforts to clean up the BP oil spill.
The Taiwanese vessel - called "A Whale" - is designed to vacuum up oily water, separate the oil and return the water to the sea.
Mr Grantham told Reuters news agency: "After an initial 48-hour testing period results remain inconclusive in light of the rough sea state we are encountering.
"Therefore, working in close coordination with the US Coast Guard, we will be undertaking an additional testing period to make operational and technological adjustments aimed at improving skimming effectiveness given the actual conditions we are encountering in the Gulf," he said.
He noted that smaller skimming vessels were also struggling to operate in the conditions.
Oil has been gushing from a ruptured well in the Gulf of Mexico since 22 April, after BP's Deepwater Horizon rig exploded and later 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 a 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," Mr Grantham said.
Adm 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.