The cap placed on the oil well gusher in the Gulf is holding - so far.

The Washington Post:

As part of what BP calls an "integrity test," a robotic submersible slowly closed a valve on the well's new sealing cap. That choked the flow until the plume, a fixture of cable TV and many a nightmare, disappeared. The technological breakthrough came 87 days into the crisis, which began with the April 20 blowout that killed 11 workers and sent the burning rig Deepwater Horizon to the bottom of the gulf.

BP could nix the test at any moment and reopen the well. Whether the well remains "shut in," to use the industry term, depends on the analysis of pressures in the well. Engineers and scientists hope to see high pressure hold steady during the 48-hour period allotted for the test. That would suggest that the well bore is physically intact. Lower pressure would hint of breaches in the casing and leakage into the surrounding rock.

The initial pressure readings are in an ambiguous range, and officials will have to make a difficult judgment call on whether to keep the well shut in or reopen it, according to Tom Hunter, retired director of the Sandia National Laboratories and a member of the federal government's scientific team overseeing the test.

"If it were a lot higher, it would be an easier decision to make," Hunter said.

If the metal casing lining the hole has cracked under the tremendous pressure, there is a likelihood that oil will also be leaking in the area surrounding the hole. If that's the case, the only way to stop the gusher from spilling more millions of gallons into the Gulf will be when the relief wells are finished - probably sometime in the fall.

The next 48 hours will tell the tale.