It will still be another two days before BP knows if its "top kill" maneuver to end an oil spill worked.

It will still be another two days before BP knows if its "top kill" maneuver to end the Gulf of Mexico oil spill worked, the company's CEO said Friday.

BP CEO Tony Hayward said it will probably be another 48 hours before the company can say for sure whether a risky maneuver to cap its gushing undersea well is successful.

"I think it's probably 48 hours before we'll have a conclusive view," Hayward said on CNN this morning. "I know that's frustrating for everyone. I am probably more frustrated than many. I want to get this thing done and know as soon as we possibly can. We are doing everything we can to achieve that."

The oil company began, with federal permission, the procedure on Wednesday to pump heavy drilling mud into a leaking well, in an effort to stop the flow of oil and cement the leak shut. 

While the "top kill" effort appeared to have some early success, it was halted after engineers discovered that drilling fluid was escaping. The effort resumed late Thursday night. 

Adm. Thad Allen, the commander in charge of the response to the spill, said the next 12 to 18 hours would be "very critical" in determining the success of the operation.

"I think the real challenge today is going to be to sustain the mud on top of the hydrocarbons, and reduce the pressure to the point where they could actually put a cement plug in," Allen said on "Good Morning America" on ABC. "And I think it'll be very critical in the next 12 to 18 hours."

President Barack Obama is traveling to Louisiana on Friday to survey the damage from the spill to Gulf coastlines, and receive briefings on the effort to stop the flow.

Cross-posted to the Briefing Room.

Cross-posted to the E2 Wire.