The Deepwater Horizon well is situated 1500 m below the surface of the Gulf of Mexico. The hydrostatic pressure is approximately given by the simple formula of where is the pressure of the atmosphere, is the density of water, and is the gravitational acceleration. Putting the numbers together gives , which is or about 150 times atmospheric pressure. Hence, the oil and natural gas must be under tremendous pressure to be able to leak out of the well at all. It’s no wonder the Top Kill operation, where mud was pumped in at high pressure, did not work.
Currently, it is estimated that the leak rate is somewhere between 10,000 and 100,000 barrels of oil per day. A barrel of oil is 159 litres or 0.159 cubic metres. So basically 1600 to 16000 cubic metres of oil is leaking each day. This amounts to a cube with sides of about 11 metres for the lower value and 25 metres for the upper one, which is about the length of a basketball court. However, assuming that the oil forms a layer on the surface of the ocean that is 0.001 mm thick, this then corresponds to a slick with an area between 1,600 to 16,000 square kilometres. Given that the leak has been going on for almost two months and the Gulf of Mexico is 160,000 square kilometres, this implies that the slick is either very thick, oil has started to wash up on shore, or a lot of the oil is still under the surface.