BP spokesman John Barnes says crews launched the so-called "static kill" process Tuesday at 3 p.m. Central time to plug up the well and then possibly seal it with cement.
The well has leaked millions of gallons of oil into the Gulf since a BP rig exploded in April and killed 11 workers. The company was able to bottle up the leak last month with a cap, but engineers always considered that a temporary solution.
BP engineers say the static kill may permanently plug the well but they may not know for sure until they finish a relief well later this month.
They then plan to pump mud and cement through that to permanently suffocate the source of the oil.
