BP’s stricken well in the Gulf of Mexico spilled an estimated 4.4M barrels of oil into the ocean before it was capped, the first objective scientific study of the disaster has concluded.
The quantity of oil which poured from the Deepwater Horizon well for three months was enough to fill 700,000 cubic metres.
The gushing well head was capped in July, but the full impact of the world’s worst oil catastrophe is still being unravelled.
Researchers yesterday reported the findings of an independent assessment of the size of the spill in the journal Science.
By analysing underwater video images of the leak, they calculated that up to 58,000 barrels of oil - possibly more - escaped daily until the first effective cap was installed on 15 July. One barrel of oil is equivalent to 190l.
BP has been strongly criticised over the disaster, which occurred on 20 April when escaping methane triggered an explosion that ripped through the oil platform killing 11 workers and injuring 17 others.
The study divides the flow rate into two periods. The first, from 22 April to 3 June, saw 56,000 barrels of oil a day gush from a jagged break in the riser, the pipe extending from the drilling platform to the sea floor.
After 3 June, the riser was cut and oil temporarily poured into the ocean unimpeded. At this stage the flow rate of the leak rose to around 68,000 barrels.
The authors subtracted 804,877 barrels collected by BP at the site to come up with their final figure of 4.4M barrels.
Scientists initially greatly underestimated the extent of the leak and the figures were later revised upwards, but objective data was lacking.
The latest estimate, which has a 20% margin of error, is broadly in line with the US government’s most recent assessment of 4.1M barrels.
Timothy Crone, from Columbia University, New York, who co-led the new study, said: “We wanted to do an independent estimate because people had the sense that the numbers out there were not necessarily accurate.”
The researchers pointed out that their conclusions rested on just a few short clips of high resolution video - all that had been released to the public so far by BP and the US government.
Video of several other leaks from smaller holes further up the pipe was not included in the analysis, so the true figures could be larger.