The success of BP's latest attempt to completely cap its leaking oil well isn't just important to the ecosystem and residents of the Gulf of Mexico who have suffered 82 days of devastating pollution. There are two very good reasons why BP needs this to work.

Firstly, crunch time is approaching for BP's only remaining option for permanently capping the leak -- the relief wells. The drilling of a relief well, which intersects the original well bore deep beneath the ground and pumps it full of heavy mud and cement to kill the leak, is a tried and tested oil industry technique. It's also very challenging.

BP's drilling engineers must intersect perfectly with a well bore around seven inches in diameter some 18,000 feet below them. Imagine trying to pick up a pea in the end of a mile long drinking straw and you've got some idea of the level of the challenge.

The last time a relief well was drilled to cap an oil leak -- the Montara rig blowout off the northwest coast of Australia late in 2009 -- it took five attemps over the course of a month to hit the well bore. Given the level of public outrage in the U.S., it's hard to imagine people sitting patiently if BP faces a similar timetable in its efforts to kill the leak. However, if the company can demonstrate that the cap is preventing all of the oil leaking into the Gulf, it will have far more breathing space to get the job done.

Secondly, if BP is able to capture 100% of the oil leaking from the Macondo well, for the first time it will be able to accurately answer the controversial question -- just how big is the leak. This may seem academic to the people who can see with their own eyes oil that has washed onto their beaches, but it is crucial in determining how many billions of dollars BP will pay in fines.