Anything that is under pressure and then loses pressure has to give, just like when a basketball or soccer ball loses enough air pressure that a quadrant section of the ball inevitably ends up caving inward.
Long before this oil spill happened, it was observed that mass drilling exploration of the Gulf sea area - with a current count of 3,858 drilling operations - was beginning to compromise the integrity of the tectonic plates underlying the ocean floor due to the vacating of oil and gas. On September 11, 2006, an extremely rare earthquake - at a 6.0 magnitude - struck the Gulf Sea area, for which the epicenter of the quake was in fact underneath the tectonic plate region.
As a normal expectation of oil drilling operations, there are the so-called "sympathetic leaks" that take place often hundreds of miles from where the actual well was drilled. As such, it was again long before this actual oil spillage disaster began that small fissures of leaking oil could be found a hundred or more miles away from the drill site, including where limited episodes of oil tar balls would periodically wash up along the beaches of Louisiana and Florida.
The suggested sympathetic fissures of leaking oil begin on a spontaneous basis, but the apparent cause of the fissures is due to the fact of the compromised vault of pressure that was manifested through drilling into the oil and gas deposit in the first place. In other words, the loss of pressurization at one location a hundred or more miles away creates a ripple effect of lost pressurization along the entire boundary line of the oil and gas deposit. This cause and effect situation results in the ongoing and systemic collapse of surrounding geologic structures that end up producing cracks in the ocean floor and thus the ensuing release of oil and gas in areas that are not technically being drilled.
The simple analogy to this is when the muscles of the body start to deteriorate and become compromised that the problem invariably leads to a loss of support for the skeletal system that the muscles had been supporting -- and the skeleton effectively begins falling apart and crumbling. But as for periodic episodes of oil tar balls washing up along Louisiana and Florida beaches, these instances have been occurring for many years now.
An item of rhetoric that I don't have a citation for here is that it was long ago given as either the official or unofficial estimates of BP that this Deepwater Horizon well had the capacity to release a maximum of 167-thousand barrels of oil per day based upon a complete loss of the well head at the ocean floor. However, what I tended to personally presume from that consideration is that BP was speaking simply of a fully compromised well head in and of itself, but NOT that they were talking about a collapse - or caving in - of the ocean floor. I am just guessing here in suspecting that an actual collapse of the sea floor itself would not nearly be the same as simply losing the well head; and that such a collapse may more accurately result in the release of tens of millions of barrels of oil per day.
Geologic estimates have been made to suggest that this particular oil deposit in the Gulf sea is either the first or second largest such deposit yet discovered at an estimated 25-thousand square miles; and that by definition it is more of a natural gas well than an oil well, since it is believed where the deposit contains upwards of 10-thousand times more natural gas than it does actual oil. At 25-thousand square miles, the area of the well is larger than the circumference of the earth, which is 22-thousand miles. As such, and without any question, there would be enough oil in this one deposit alone to completely pollute all the oceans of the earth, including all of the freshwater rivers, lakes and streams.
The interesting misnomer apparently being perpetuated by the media - including to view the article link that you've posted here - is that this ongoing oil spillage is somehow only going to adversely affect the greater Gulf Coast region and fundamentally be contained to it, but that is simply not true beyond a certain point. The reason it is not true is because all the oceans of the world operate on what is referred to as a Global Conveyor Belt system in which all the oceans very effectively spill into each other.
Beyond a certain point, which I fear is not all that far into the future at a personal estimation of perhaps two (2) years, this single oil spill has the capacity to completely destroy all the waters of the earth in short order.
The website addresses listed below offer various citations to support my position in answering this question. The third address in the list points to an image of the noted oceanic Global Conveyor Belt system, which offers to clearly illustrate how the waterways of the world are invariably interconnected and feed into each other...