Government officials said Friday morning that the flow of oil from an offshore BP well has stopped after the oil company performed a “top kill” procedure. Watch the live feed of the procedure.

Adm. Thad Allen of the U.S. Coast Guard said the procedure stopped the flow of oil caused by the explosion of the Deepwater Horizon on April 20, but said the next 12 to 18 hours will be crucial to make sure the top kill worked.

A top kill procedure involves pumping heavy drilling fluid, called mud, into the well until the flow of oil stops. Then, concrete is pumped into the well to plug it completely. Click here for how the procedure works.

The CEO of BP, Tony Hayward, said there’s a 60 to 70 percent chance that the procedure will be successful and the company needs another 48 hours to know if the spill is completely stopped, according to a MSNBC report.

Hayward also said the spill is an “environmental catastrophe,” after scientists determined that the Deepwater Horizon spill was bigger than the Exxon Valdez spill in Alaska and in fact the biggest in U.S. history. Read more.

In a press conference Thursday, President Barack Obama said he would head to the Gulf Coast today. Critics have said that Obama has not done enough to remedy the spill. Though Obama said he thought his administration was doing its best in handling the situation, he said the spill response is ultimately his responsibility.

See photos of the spill.