British oil giant BP yesterday said that it has successfully placed a new sealing cap on the Deep Water Horizon oil leak and has started to conduct tests to find out whether the leak in the Gulf of Mexico could be stopped completely.

Following installation of the capping stack BP will start conducting well integrity test from today on the Mocondo oil well situated a mile below the surface of the sea to find out whether the new sealing cap is functioning.

BP said that for the duration of the test, which will be a minimum of 6 hours and could extend up to 48 hours, the three ram capping stack will be closed and all sub-sea containment systems will be temporarily suspended, effectively shutting in the well.

''It is expected, although cannot be assured, that no oil will be released to the ocean for the duration of the test. This will not however be an indication that flow from the wellbore have been permanently stopped,'' BP said in a release.

The oil giant however warned that the sealing cap system has never been deployed before at these depths or under these conditions, and its efficiency and ability to contain the oil and gas cannot be assured.

By conducting the tests, BP wants to find out whether the pressure in the well is rising and holding, which indicates that the well is not damaged and oil is not leaking.

BP will then consult with US government scientists on keeping the valves closed thereby shutting the well - similar to putting a cap on a soft drink bottle.

BP has tried many containment methods to stop the leak for more than 12 weeks after the Deepwater Horizon rig exploded and sank on 20 April 2010, killing 11 workers and spilling between 35,000 and 60,000 barrels of oil, according to US government and independent scientists, although BP refutes these figures.

The capping of the oil well if successful will still be a temporary measure until a permanent solution like drilling of two relief wells that should be completed by the middle of next month.

BP said, ''Relief well operations continue throughout this period and remain the sole means to permanently seal and isolate the well.''