BP today ran a test of its new containment cap on the geyser of oil that's been leaking into the Gulf of Mexico since April. Apparently it's working, and the flow of oil has been stopped, at least for now. Why did this one get the job done?
Simple answer: size. The new cap is tighter-fitting than the previous one, and it's larger, capable of holding more oil and siphoning it to more containment ships (up to four). BP also appears to be no longer underestimating the flow of oil (the previous attempt at capping the spill may have actually increased the flow), which no doubt played a factor.
Of course, the cap isn't meant to be a permanent solution, and this kind of cap has apparently never been tested at the depth of the Deepwater Horizon blowout. The only thing that can stop the spill are the two relief wells, begun on May 4, that will plug the leak with mud and cement. Well, the only thing other than a nuke.