BP successfully stopped the flow of oil from its blown-out Macondo well for the first time yesterday, but whether that augurs a long-term fix is still unclear.

Remember that the key measurement engineers were and are tracking is the pressure in the well. If the leak that was capped is the only or primary leak, capping it would force pressure to build up as oil tries to push out. High-pressure is a good thing, though. The alternative is that the well acts like a crude hydra: you cap one leak, and others spring up.

"Retired Coast Guard Adm. Thad Allen, the national incident commander, has said that a pressure reading of 8,000 or 9,000 pounds per square inch would be ideal, while a reading below 6,000 psi might indicate leakage," The Washington Post's Joel Achenbach writes this morning.

So, what is the pressure, then? Unfortunately, it falls within the ambiguous middle range between 6,000 and 8,000, at least so far.

"[BP vice president Kent] Wells reported that the pressure was at 6,700 psi on Friday, about the same level as it was on Thursday, according to Tom Hunter, a member of the federal scientific team that is overseeing the test."

Hunter went on to say that it was "premature" to make a determination about whether the oil monster has just one head or many.

Check out our recent update on how the oil spill changed the country.