Today, nearly three and a half months since the sinking of the Deepwater Horizon, the oil-spill response has been getting an unusual amount of positive publicity. Heavy drilling mud pumped down into the well as part of the static kill is successfully holding back the oil pressure, and the government has released a scientific report suggesting that 75 percent of the 4.9 million barrel spill has been collected or has been burned, has dispersed or has evaporated. Carol Browner, President Obama's energy and climate-change adviser, declared on ABC's Good Morning America that "the majority of the oil appears to be gone," a sentiment that has been widely echoed in news coverage. But while the results of the report are certainly promising, that conclusion could be misleading.
To be precise, the report indicates that 50 percent of the oil is gone—17 percent was collected directly from the wellhead, 8 percent has been skimmed or burned, and 25 percent has evaporated or dissolved. Of the remainder, 24 percent has been dispersed, either naturally (16 percent, by the force with which oil left the wellhead, much like spray from an aerosol can) or through the use of chemical dispersants (8 percent). The final 26 percent remains unaccounted for, and has either washed ashore or remains lurking in the sea.
But because the degradation process is hard to track, what all this means is that up to 50 percent—or nearly 2.5 million barrels—of the oil that was released could conceivably still be out there. This includes 1.2 million barrels of dispersed oil that is, as the report notes, "in the process of being degraded." Some of it may be gone by now, gobbled up by oil-eating microbes, but it's unclear how fast this biodegradation is occurring. Even under favorable conditions, the process can be slow.
Furthermore, even if you make the assumption that all of the dispersed oil has already degraded, that means that 1.3 million barrels remain out there in the environment. That's five times the amount of oil that was released during the 1989 Exxon Valdez spill, which killed a whopping 250,000 seabirds, in addition to thousands of sea otters and hundreds of seals. So the new report is indeed good news, since the situation could be worse—but there's still more than enough Deepwater Horizon oil out there to wreak considerable environmental damage.