The apparent success of the static kill had some along the Gulf curious about why BP waited so long to try it.
But the static kill - also known as bullheading - probably would not have worked without the cap in place. It involved slowly pumping the mud from a ship down lines running to the top of the ruptured well a mile (two kilometers) below, and a similar effort failed in May when the mud couldn't overcome the flow of oil.
Workers stopped pumping mud in after about eight hours of static kill work and were monitoring the well to ensure it remained stable, BP said.
Even politicians expressed concern that BP and the federal government will need to stay focused on the cleanup and long-term monitoring of the Gulf's marine life.
"This is a positive step," said Louisiana Gov. Bobby Jindal, "But this crisis is not over for Louisiana until the well is permanently capped and our coasts and wetlands are fully restored to their pre-spill status and our people can resume their way of life."