COCODRIE, La.—Five million barrels of oil seems like a lot. That is approximately what spewed from the blowout at BP's Macondo well last year, about enough to fill an area the size of an American football field more than 90 meters deep—and much of it has gone missing.

"There's a lot of water out there for the oil to be in," notes toxicologist Scott Miles of Louisiana State University (L.S.U.), who has researched the fate of the oil from last year's spill. Where is it? "Your guess is as good as mine."

Last August 4, the federal government released an accounting of all that oil, updating it in November. According to that report, ships skimmed 160,000 barrels of oil and BP's various efforts captured another 820,000 barrels before it escaped into the sea. More than 400 burnings of concentrated slicks moved 260,000 barrels from water to air. The application of 1.8 million gallons of COREXIT dispersed 770,000 barrels of the oil spill while the simple mechanics of the oil and gas entering the water 1,500 meters down through a relatively narrow pipe dispersed another 630,000 barrels. Nearly a quarter of the oil evaporated or dissolved in the water or air. That leaves just 1.1 million barrels lost at sea—or hidden in the shoreline. After all, by August 20, no oil slicks from the Macondo well blowout could be detected on the surface of the Gulf of Mexico.

"The numbers are not unreasonable and it may very well be correct," says biologist Christopher D'Elia, dean of the School of the Coast and Environment at L.S.U. But "putting a budget together [for an oil spill] is really hard to do. Any one of these things could be off." And some scientists put the number of remaining oil much higher—as much as four million of those barrels are still out there, according to the most pessimistic estimates.

Oil eaters
There is no doubt that the hydrocarbon-eating microbes of the Gulf of Mexico had a feast last year. Their efforts may have disposed of the more than 1.4 million barrels of oil broken up into small droplets. "Where we have oxygen and light and heat, the oil will degrade rapidly," says marine and atmospheric scientist Alexander Kolker of the Louisiana Universities Marine Consortium. "Where we don't have those things it will be slower."

Those microbes did much of their work in the deep as vast plumes of oil formed under the water, contrary to the protestations of then BP chief executive Tony Hayward and the expectations of National Oceanic and Atmospheric Administration (NOAA) head Jane Lubchenco. Scientists documented several such plumes, including one that was 200-meters high, two-kilometers wide and 35-kilometers long. That plume persisted at least through June, suggesting that microbes were not working as quickly as might have been hoped—although other research found much higher rates of microbe oil-munching, starting with the natural gas components of the blowout. 

The oil that did make the trip all the way to the surface, took roughly two hours to do so and created a slick at least a kilometer away from the wellhead itself, depending on currents. And whether in the deep or on the surface, all of that oil found itself among some 643 quadrillion gallons of water—a lot of ocean to get lost in.

Yet, NOAA testing found enough of the more than 1,000 different hydrocarbons in oil to keep areas closed to fishing until April 19 this year—almost exactly a year after the spill started. "Oil is still present," explains biologist Martin Bourgeois of the Louisiana Department of Wildlife and Fisheries.

That is not entirely the fault of the consortium of companies involved in the Macondo well blowout. The Gulf of Mexico endures a slew of spills every year, in addition to the natural oil seeps that release as much as 1.4 million barrels of oil annually. Much of that oil—and likely the oil from BP's Macondo well blowout—ends up sinking to the seafloor, either directly or inside dead oil-eating microbes or oil-containing plankton. The biggest Gulf oil spill prior to BP's blowout—Ixtoc 1—saw roughly 25 percent of 3.5 million barrels of oil sink to the bottom. "Has this oil dropped to the floor?" Miles asks, noting that some deep-sea sampling suggests it has. "Oil may be getting heavier and heavier and dropping to the floor."

Persistent oil
It's not just the oil that persists, of course. At least one of the compounds in the 300 oil tankers worth of dispersants used to break up the spilled oil is still out there—dioctyl sulfosuccinate sodium salt, or DOSS, which is the active ingredient in COREXIT. "It didn't seem to be significantly degraded even through September," says chemical oceanographer Elizabeth Kujawinski of the Woods Hole Oceanographic Institution, who studied its fate in water samples. "This one component lasts. I don't know what happened to the rest."

And oil can still be found in the Louisiana marshland, in places like Bay Jimmy and Elmer's Island. That oil will be there for a very long time, based on the experience of previous oil spills such as the Florida oil barge mishap off the coast of Cape Cod or the Exxon Valdez tanker spill in Prince William Sound, Alaska. "The sediments provided a long-term refugium for toxic levels of oil," says biologist Andrew Whitehead of L.S.U.

And there's no question that oil and gas generally will remain a big part of Louisiana for the foreseeable future. Billboards promoting legal help with denied BP claims alternate with advertisements for work in the offshore oil and gas industry on the highways leading to the coast. "Our oil field is so important to our parish, we had to ask, 'Please let us drill again,' which is kind of hard to explain," says Terrebonne Parish President Michel Claudet. Despite the unknowns about the long-term effects of BP's Macondo well blowout, "we don't have any problems with them drilling again."

Ultimately, five million barrels is just not that much oil. Gulf of Mexico offshore oil wells produce 1.6 million barrels of oil every day and the U.S. consumes more than 20 million barrels daily. In fact, the Louisiana gulf coast endures spills year after year and month after month. "There are spills happening every day out in the Gulf of Mexico," notes Janelle Robbins, associate director for Waterkeeper. "There's a lot of oil unaccounted for, it's not gone. It's out there someplace but finding it is going to be tricky. And some people would rather not find it at all."

As the Congressional Research Service's Jonathan Ramseur wrote in his report on the fate of the oil (pdf) from December 16: "Months later it is unknown what happened to the oil that remained….It is debatable whether the fate of the remaining oil will ever be established conclusively."

Editor's Note: Reporting for this article took place as a result of a fellowship from the Metcalf Institute for Marine and Environmental Reporting at the University of Rhode Island.

13 Comments

1. 1. Soccerdad 03:14 PM 4/25/11

   The title of this article is riduculous. If one can get this thing to balance as closely as it has, that's pretty darn good. The obvious answer is that more burned or evaporated or was eaten by microbes than calculated. This oil is not "missing".

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2. 2. lauriewiegler 04:18 PM 4/25/11

   I realize it's a popular subject, "Where did the oil go?" and your measurement is really well researched. But is anyone looking at the dispersant applications themselves and how so much is unknown about what occurred on the VOO boats. If it took the EPA a long time to share the ingredients in Corexit, who knows what else is being hidden. I've covered the spill since last July, and a far bigger concern than how much oil is how many lives have been affected, how many dead animals are in the ocean, and how much coverup occurred.
   That said, I love your reporting and realize this is a very important subject. I just don't think we are getting all the information from "official" sources, and having written at least 300 stories on this I know we are not.
   

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3. 3. dbiello 05:14 PM 4/25/11

   Laurie--You are absolutely right that those are all interesting stories. I just did wildlife:
   
   http://www.scientificamerican.com/article.cfm?id=how-did-bp-oil-spill-affect-gulf-of-mexico-wildlife-and-ecosystems
   
   and health implications will be an ongoing coverage area for us:
   
   http://www.scientificamerican.com/article.cfm?id=did-bp-oil-spill-ruin-gulf-seafood
   
   mental health particularly. As for COREXIT, stay tuned...

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4. 4. Postman1 05:30 PM 4/25/11

   I remember at the time that the 'estimates' of the amount leaking were extremely varied, and there was no meter measuring the output, so maybe the estimates are just off that much.

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5. 5. HubertB 08:45 PM 4/25/11

   Simply because it took a long time for oil to break down in cold Alaska does not mean it will take a long time in hot Louisiana. Eskimos need far fewer iceboxes than do Cajuns. Comparing biological processes when the temperature difference is greater than 30 degrees Fahrenheit leaves something out. The oil might disperse much faster than it has in Alaska.
   Since the Gulf is warmer than the Atlantic at the same longitude, biological processes might have eaten the oil at a faster pace than predicted by a team from Woods Hole in frozen Massachusetts.

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6. 6. baranof 11:10 AM 4/26/11

   you mentioned one of the plumes being 200-meters high, 2-kilometers wide and 35-kilometers long. So that that one plume is 14 billion cubic meters or 3.7 trillion gallons of oil/water? Rather than plume, maybe there is a better word to describe minute traces of oil in the water column?

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7. 7. independentamerica 11:58 AM 4/26/11

   according to BP those 1.1m barrels never spilled, claimants are happy, and Feinberg is fair.
   
   http://www.bpandfeinbergbankruptedus.com

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8. 8. poweringanation in reply to lauriewiegler 03:41 PM 4/26/11

   These number are relatively low given the size of the Atlantic but, as lauriewiegler said, they must be put in context with the effects on the ecosystem. I've recently read an article saying that the number of dead dolphins washing up on the Gulf shores is way higher than average, for example. And many of these effects may not emerge for quite some time.
   
   We investigated the spill from a community perspective. Does anyone know where to find good stats re: the ecosystem?

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9. 9. tiddas in reply to poweringanation 01:09 AM 4/27/11

   Thank you. Media really has let people down by failing to describe how the Gulf works biologically and how much of our natural heritage the BP spew annihilated.

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10. 10. tiddas 01:13 AM 4/27/11

    I can't help being snarky: Maybe the "missing" oil is in the brains of the Gulf Coast state residents begging for the oil economy to come back, continue, be expanded.
    
    Actually, I think this is a publicity myth. If polled, I imagine 99% of Gulf Coast residents who don't directly benefit from the oil industry would say "bring us a diverse green economy with a cleaned up ecosystem."

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11. 11. 14ihlti 03:40 PM 4/28/11

    Soccerdad is Incorrect in My opinion

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12. 12. david.jackson3 in reply to poweringanation 05:19 AM 4/29/11

    "I've recently read an article saying that the number of dead dolphins washing up on the Gulf shores is way higher than average, for example."
    
    Gee. In my dictionary, an average means that sometimes things will be greater, and other time they will be smaller. What is your point please?

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13. 13. chacesmith 12:59 PM 6/5/11

    The EPA has misused public funds, and defrauded the public in the Gulf states by only allowing Exxons toxic products that sink oil and spread the adverse impacts of the oil. The EPA uses excuses to try to prevent sound safe, non toxic proven technology such as OSE II. The EPA is violating the clean water act, and their own charter with non scientific excuse to not use OSE II. OSE II has had the US EPA test OSE II's toxicity on over 12 different species, proving OSE II has a toxicity value over 1900 ppm, the average toxicity for OSE II with EPA's test is over 5,000 ppm, compared to corexit, which with 32 ppm or lower, the lower number being more toxic. OSE II has been ingested on TV to show how safe it is to humans, and the EPA's test substantiates OSE II end point of converting oil to CO2 and water. Dr. Tsao, in charge of BP's BCST successfully tested OSE II is is attempting to implement OSE II into the marshes and beaches. The EPA has allowed the eco system to be destroyed, millions of species of marine and wildlife to be destroyed, the gulf states economics have been devastated, while they try to make excuses, and justify corexit, who's own labels state they are both potentially lethal to humans and have proven to be so. The EPA is using tax payer money to justify their decision to allow the use of the two toxic corexits, this is not their job, and a misuse of public funds. The EPA and NOAA have told people repeatably the water and seafood is safe, by manipulating tests, which is another misuse of publics funds to defraud the American public. All independent testing of the water, sea bed sediments, and seafood has proven the environment has been made toxic by EPA's decisions. There is proof the seabed was fractured as bad as the reports in May and June of 2010 stated, since there is enormous amounts of new oil coming ashore daily, and is expected to for the next 20-30 years. There is also evidence that corexit is being applied daily and is bio accumulating in the water, and on the seabed. The entire response has been inadequate, and needs to be changed as soon as possible. It is time the EPA enforce the very rules they promulgate, use the best proven technology to address this spill so that the impact to the gulf states ecology and economy can be returned to pre spill conditions. The EPA has afforded an illegal monopoly for Exxon's horrific toxic products, it is time the US EPA stop misusing public funds, defrauding the public, and change to an adequate response they themselves have utilized in the past OIL SPILL EATER II

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