BP's Thunder Horse oil platform, one of its biggest under development, is listing after Hurricane Dennis battered the Gulf of Mexico.
Deep water oil platforms are vulnerable to extremes of weather
The platform sits in deep water about 150 miles south of New Orleans and was evacuated on Friday ahead of the storm.
BP said the cause of the problem is unknown, and there has been no leakage of fuel or other hazardous substances.
Thunder Horse was set to start pumping oil later this year, and peak output was expected at 250,000 barrels a day.
BP said it was not clear if the current problem would put back the planned start date.
"I don't think we know enough yet to say how this would affect the start of the field," said BP spokesman Ronnie Chappell.
Mr Chappell said that platform may be listing because of excess water in its ballast tanks and there may be little or no structural damage.
Hurricane Dennis has ripped across Cuba and Haiti, killing at least 27 people, before coming ashore in the US.
At least four people are reported to have died in the US, where Florida, Mississippi and Alabama have been declared disaster zones.
About 1.4 million people were evacuated ahead of its arrival in the US.
The storm has since lost some of its power and has been downgraded to a tropical depression.
The Gulf of Mexico provides 30% of US oil output, and there had been concerns that any disruption to supply would push the price of crude to record levels.