Sometime within the next two weeks the free-flowing Deepwater Horizon well could surpass the second largest oil spill in history. Indeed, if we assume the highest independently measured estimates of the leak’s flow rate, Deepwater Horizon may have already released 84% of the total petroleum that was dumped into the Gulf of Mexico by the Ixtoc I, a similar rig blow-out that occurred in 1979.

One of the highest estimates to date has been made by Mirko Gamba, a post-doctoral researcher at Stanford. Using a computer imagery analysis tool called Particle Image Velocimetry (PIV), Gamba has measured the parameters of the flow at between 30,000 and 95,000 barrels per day (bpd). At 30,000 bpd it would take approximately 117 days for Deepwater Horizon’s total oil release to exceed Ixtoc I. As of Thursday, May 20, 31 days have elapsed. At the upper-limit of Gamba’s range, Deepwater Horizon will become the second largest oil spill in history on Wednesday, May 26.

Most independent estimates of the Deepwater Horizon’s flow rate are five to nineteen times as large as BP’s 5000 bpd estimate. Nevertheless, BP has insisted on this figure, which the National Oceanographic and Atmospheric Administration has used also.

These measurements are so disproportionate, however, that many scientists have voiced concern about BP’s refusal to make more data public, as well as the companies restriction of further attempts to gauge the leak’s flow rate.

Here is a simple chart comparing Deepwater Horizon to Ixtoc I and other similar ocean rig blow-outs.

Given that almost one month has elapsed and the well has not been capped, it is likely the leak will continue to flow at high rates until relief wells are successfully drilled. Relief wells typically take weeks or months to finish depending on the depths and conditions confronted. For Deepwater Horizon this process may take another two-three months. Combined with a flow rate that exceeds 20,000 bpd average over this time frame the leak will easily surpass Ixtoc I.

There is a remote probability that Deepwater Horizon could even surpass the 10+ million barrel spill of the Persian Gulf War, still measured as the largest in world history.