Questions raised over volume of leaked BP oil

Initially, officials claimed that the flow could not be measured. Then, as public pressure for information mounted, they looked for ways to measure it and started producing estimates: at first 1,000 barrels a day, then 5,000, then 12,000 to 19,000, then upward from there.

Now, using a new technique to analyse underwater video of the well riser, scientists say it leaked some 56,000 to 68,000 barrels daily - maybe more - until the first effective cap was installed on 15 July.

Their estimate of the total oil escaped into the open ocean is some 4.4m barrels - close to the most recent consensus of US government advisors, whose methods have not been detailed publicly.

’We wanted to do an independent estimate because people had the sense that the numbers out there were not necessarily accurate,’ said Timothy Crone, a marine geophysicist at Columbia University’s Lamont-Doherty Earth Observatory.

After BP and government officials downplayed the possibility or importance of measurements, a number of scientists, environmental groups and legal experts pointed out that the information was needed to determine both short- and long-term responses, as well as monetary liability.