Crews working to seal BP's blown-out oil well in the Gulf of Mexico need to complete just one more test before plugging it once and for all. Workers started filling the well with cement on Friday.

It hardened on Saturday, leaving one final pressure test. This is an important milestone for the weary residents of the Gulf Coast giving them an assurance that not a trickle of oil will ever seep from the well.

The tragedy began April 20, when an explosion killed 11 workers, sank a drilling rig and led to the worst offshore oil spill in U.S. history.