My biggest fear was that capping the leak might expose damage deeper down the casing, causing oil to seep up uncontrollably all over the place. It seems like these fears might be coming true.

On Sunday, engineers discovered oil seeping deep out of the seafloor “at a distance” from the wellhead and possible “anomalies” at the wellhead.(via)

Pressure in the well was not as high as the government of BP expected, and it might be that some of the oil is working its way out the side of the bore. If this happens it might be impossible to keep the cap on. The last thing anyone wants is to have a million uncontrolled tiny leaks all over the place instead of one large more controllable one.