The official estimate of the amount of oil that leaked into the Gulf of Mexico before BP managed to cap its ‘MC252’ well has again been revised upwards. The resulting new figure makes the incident the worst accidental spill in history.

US scientists now think that at the start of the disaster 62,000 barrels of oil a day were escaping the well, which began leaking after the explosion and sinking of the Deepwater Horizon drilling rig. Although this fell to 53,000 barrels per day by the time the well was capped on 15 July, a total of 4.9 million barrels probably escaped the well (press release).

Initially it was claimed that a mere 1,000 barrels per day were escaping (the history of the endlessly increasing estimates is contained in the original ‘it’s worse than you thought (again)’ blog post).

Of the 4.9 million barrels that leaked, some 800,000 were captured by BP, meaning ‘only’ 4.1 million barrels actually ended up polluting the Gulf. This is still more than the previous largest ever accidental spill – the Ixtoc 1 disaster, which released around 3.5 million barrels in the 1970s. Deliberate spilling during the first Gulf War is thought to have resulted in about 5 million barrels of spillage.

In other news, BP is still preparing for the ‘static kill’ of the well. This will involve attempting to permanently seal the well by forcing heavy mud downwards to drive back oil into the reservoir and allow the whole thing to be sealed off with cement. This is similar to the ‘top kill’ attempted earlier, except that the well is no longer flowing – hence ‘static’ (BP briefing).

If the static kill is successful a decision will have to be made as to whether to continue with the relief wells, which were previously thought to be the final answer to the leak.

Image: Q4000 vessel (shown centre) undertaking preparations for the ‘static kill’ / US Coast Guard photograph by Petty Officer 1st Class Adam Eggers.