British energy group BP said that the Gulf of Mexico oil spill has cost it $450m so far, up by $100m from the figure reported earlier this week. The oil spill spend includes the cost of spill response, containment, relief well drilling, commitments to the Gulf Coast States, settlements and federal costs.

BP has said that it is continuing its subsea source control and containment efforts to check the flow of oil from the well through interventions via the blow out preventer (BOP) and to contain the flow of oil at source to reduce the amount spreading on the surface.

Further investigation of the failed BOP, using remotely-operated vehicles and a variety of diagnostic techniques, has increased its understanding of the condition of the BOP and allowed planning to continue for a number of potential interventions, including for a so-called ‘top kill’ of the well, the company said.

This would involve first injecting material of varying densities and sizes (also known as ‘junk shot’) into the internal spaces of the BOP to provide a seal, before pumping specialized heavy fluids into the well to prevent further flow up the well. Plans for this option are being developed in preparation for potential application next week.

Work to deploy a second system designed to contain the oil flow subsea has continued. A small dome or ‘top hat’ has been taken out to the well site and placed on the seabed in preparation for deployment. Such a system has never been used in water depths of 5,000ft and its successful operation is not certain, according to the company. The deployment of this system is expected to be attempted within the next few days.

Work on the first relief well, which began on May 2, continues. It is expected to take some three months to complete. The drilling rig that will drill the second relief well is currently en route to the site. Surface spill response and containment work continues to collect and disperse oil that has reached the surface of the sea.