Experts still hope to close a stuck valve that's let oil flow into the Gulf of Mexico for more than a week. But if those efforts fail, the next-best plans will take weeks more to stop the flow, officials say.

The undersea oil well, following a drilling rig's April 20 explosion 50 miles off Louisiana's coast, is spewing up to 210,000 gallons of light sweet crude a day into the Gulf, officials say.

Eleven workers from the rig are missing and presumed dead.

Part of the Gulf Coast was bracing for oily water to reach shore early Friday.

BP, the well's majority owner, has been trying to stop the flow by using remote-controlled submarines to activate a valve atop the well. But the valve, known as a blowout preventer, is not working.

A stopgap plan -- putting a chamber over the well area and sending the oil to a ship -- is unproven at that depth and could take four weeks before it's ready. And the ultimate plan -- drilling a different well to access the first and close it with concrete -- could take three months. Meanwhile, efforts to contain the spill and stop the leak are costing the well's owners about $6 million per day, BP says.