BP said on Sunday that the ruptured oil well in the Gulf of Mexico remains sealed for a third day and pressure is continuing to build in an "encouraging" way.
"Two and a half days, in the results continue to look encouraging," BP chief operating officer Doug Suttles told reporters.
He added that "the well remains shut in" and that "pressure does continue to build."
The tests involve multiple pressure readings on the wellbore that runs to the oil reservoir below the seafloor.
Engineers monitoring pressure in the well remain remain cautiously optimistic that a months-long oil spill that has created the worst environmental disaster in US history has been finally contained.
But Suttles said it is too soon to herald success in containing the spill.
"These are just early steps and it is critical that we realize we will be here for the long-term," he said.