NEW ORLEANS – The best hope for stopping the flow of oil from the blown-out well at the bottom of the Gulf of Mexico has been compared to hitting a target the size of a dinner plate with a drill more than two miles into the earth, and is anything but a sure bet on the first attempt.

Bid after bid has failed to stanch what has already become the nation's worst-ever spill, and BP PLC is readying another patchwork attempt as early as Wednesday, this one a cut-and-cap process to put a lid on the leaking wellhead so oil can be siphoned to the surface. BP said Monday it was also planning further containment efforts to supplement this week's try.

But the best-case scenario of sealing the leak is two relief wells being drilled diagonally into the gushing well — tricky business that won't be ready until August.

"The probability of them hitting it on the very first shot is virtually nil," said David Rensink, incoming president of the American Association of Petroleum Geologists, who spent most of his 39 years in the oil industry in offshore exploration. "If they get it on the first three or four shots they'd be very lucky."

The relief well drilling and temporary fixes were being watched closely by President Barack Obama, who planned to meet for the first time Tuesday with the co-chairmen of an independent commission investigating the spill. A senior administration official said the meeting will take place at the White House. The official spoke on condition of anonymity because the meeting had not been formally announced.