Andrew Revkin writes at “Dot Earth” at NYTimes.com:

The latest word from the team overseeing efforts to manage the oil gushing from the Gulf of Mexico seabed is that capturing the vast flow remains the prime goal, with chances of stopping it outright looking slim at least until early August.
Adm. Thad W. Allen of the Coast Guard, the “incident commander” in charge of operations at the wrecked well, updated reporters on a telephone conference call this morning. (Somehow the word “incident” doesn’t adequately capture an unfolding disaster, but this is all new territory in an arena attuned to “spills.”) Here are a few notable developments (a transcript should be posted later):
Several questions were asked about the integrity of the well bore, the drilled and lined hole descending several miles from the seabed to the oil and gas deposits far below. If the lining is fractured, no effort to cap the well at the top would be safe because oil could flow up through the earth outside the well with no options for suppressing it. (Think of how leaks in a pressurized garden hose worsen if you close the nozzle at the end.)
“We don’t know the exact status of the well bore,” Allen said. He said that one reason the “top kill” procedure was abandoned was the realization that the well bore could be compromised.

The rest here.