Rescuers drilling a seventh hole into the Utah mine hope to break through to a chamber where the six missing miners may have sought refuge.
The next step is to lower a robotic camera down the hole searching for any sign of the men.
They haven't been heard from since a cave-in more than three weeks ago.
Previous holes have found no sign that the men survived.
U.S. Mine Safety Chief Kevin Stricklin said rescue workers will continue searching for the men as long as there's a possibility they're alive.
Stricklin added that the mine's co-owner will decide when the final hole is drilled because he's the one paying for it.
It costs about $1-million to drill each hole.