BP officials have portrayed measurement efforts as a distraction from the real work of plugging the leak. Rep. Ed Markey of Massachusetts challenged BP's estimated flow rate in a letter to the company's leadership last week, but BP is so far standing by its 5,000 barrel a day figure. Scientists and environmentalists worry that underestimating the flow rate will skew development of oil spill response capabilities as well as the debate over offshore drilling.

Why BP is digging in its heels on this issue is unclear, given that at this point the company has little to lose -- CEO Tony Hayward has already admitted the spill may well cost him his job. The company has all available forms of technology at its feet, and, thanks to government oil-spill bailout funds, does not have to worry too much -- for now, at least -- about the cost of the clean-up.

One potential motivator for the company's behavior may involve its unprecedented use of chemical dispersants. Responders have been spraying the dispersants across the oil slick and applying them underwater as well. The discrepancy between the volume measurements based on the surface slick and those gleaned from the underwater footage may mean that the dispersants are working, breaking the oil into distinct particles before it reaches the surface in slick form.

Depending on the long-term effects the toxic chemicals could have on marine life, the dispersant approach may or may not be worth its environmental risk. But for BP, using the chemicals make perfect sense. They literally subvert the oil's damage, avoiding fouled coastlines in favor of besieged underwater ecosystems. The scientists who discovered the oil plumes found that the plumes were severely depleting oxygen levels, posing a grave risk to sea life:

Dr. Joye said the findings about declining oxygen levels were especially worrisome, since oxygen is so slow to move from the surface of the ocean to the bottom. She suspects that oil-eating bacteria are consuming the oxygen at a feverish clip as they work to break down the plumes.



While the oxygen depletion so far is not enough to kill off sea life, the possibility looms that oxygen levels could fall so low as to create large dead zones, especially at the seafloor.



If the oil-eating bacteria are in fact devouring oxygen at a harmful rate, the dispersants are most likely contributing to this process. One of the reasons for breaking the oil into smaller droplets is to facilitate oil-eating bacteria's access to it. If these bacteria are also consuming the oxygen that marine ecosystems need to survive, the dispersant effort could prove counterproductive.

But it could also change the way people remember this spill -- and how much accountability they ultimately expect for it. Once the leak is plugged and the oil is dispersed throughout the Gulf, who's to say for certain whether BP's blown well gushed 5,000 or 80,000 barrels of oil a day?

