The converted cargo ship A Whale spent the weekend attempting to separate crude oil from seawater in a 25-square-mile area north of the ruptured BP oil well at the heart of the disaster. If the test is successful, the massive vessel could play a key role in efforts to clean up the largest oil spill in U.S. history.

Initial results from tests are expected Monday, Bob Grantham, spokesman for the company that owns the ship, said.

The ship, which swallows water with oil then separates it, can skim about 21 million gallons of oil a day. That's at least 250 times the amount that modified fishing vessels currently conducting skimming operations have been able to contain, according to Taiwanese company TMT shipping, which owns the vessel.

A total of about 550 skimming vessels were out in the Gulf on Sunday, according to a spokeswoman for the Unified Command Joint Information Center in Houma, Louisiana. But with oil still pouring into the sea at a rate of tens of thousands of barrels a day, federal authorities closed a new section of the Gulf off Louisiana to fishing on Sunday.

The latest order from the National Oceanographic and Atmospheric Administration adds nearly 1,100 square miles of federal waters off Louisiana's Vermilion Bay to the off-limits zone. The new closure brings the portion of the Gulf closed to fishing due to the massive BP spill off Louisiana to 33.2 percent, NOAA reported.

The Coast Guard reported earlier Sunday that a shift in weather patterns could send more oil toward sensitive shores in Mississippi and Louisiana, and bad weather over the past few days has significantly hampered cleanup efforts.