Gulf Oil Spill – New Spill Calculation – Exxon Valdez Surpassed Today

Figure 1. US Coast Guard map showing size and appearance of oil slick on April 28, 2010.

Dr. Ian MacDonald at FSU just produced a new spill-size estimate based on the US Coast Guard aerial overflight map of the oil slick on April 28, 2010. This map shows the slick covering 1,786 square miles (4,627 square kilometers). The bottom line: on April 28 there was a total of 8.9 million gallons floating on the surface of the Gulf.

That suggests a minimum average flow rate of slightly more than 1.1 million gallons of oil (26,500 barrels) per day from the leaking well on the seafloor. Since we’re now in Day 11 of the spill, which began with a blowout and explosion on April 20, we estimate that by the end of the today 12.2 million gallons of oil, at a minimum, have been spilled into the Gulf of Mexico.

The oft-quoted official estimate for the Exxon Valdez spill is 11 million gallons, although some think that is the lower limit of the likely range. It appears that we’ve just set a very sad new record.

Here is Dr. MacDonald’s calculation:

Deepwater Horizon spill estimates derived from USCG fly-over data (28 April 2010)

These estimates of the total volume of oil released by the Deepwater Horizon spill were derived from the USCG fly-over map (Figure 1). The map was geo-referenced in Arc Map and the areas of each of the slick types (dull oil streamers, etc) were measured with a planimeter tool. Thickness estimates for each slick classification were taken from the BONN guidelines as published in the NOAA field manual (Figure 2). Conservative values were used for each slick types. Note that the predicted average layer thickness are still very small.

Figure 2. Chart of oil thickness and appearance.

A human hair is approximately 100 µm (microns). The main slick, which corresponds to
the cross-hatched area was assigned a low value of 0.5 µm. We calculate a total volume of oil for this slick as 8.94 million gallons (212,000 barrels) (Figure 3). Considering that the oil in the water on April 28 has been deposited since the blowout and explosion on April 20, the flow rate should be on the order of 26,500 barrels per day. Some fraction of the total oil released will have been evaporated or emulsified and sunk in the time since the spill began, or collected by the response crews, so this should be considered a minimum estimate.


Figure 3. Volume of oil based on Coast Guard map (Figure 1) and thickness (Figure 2).

UPDATE 5/1/10 5:15 pm – Lots of cloud and haze but this afternoon’s MODIS satellite image shows the main body of the oil slick around the leaking well location.

36 replies
  1. John says:

    Sorry, we were having formatting difficulties getting this posted.

    See our Montara spill estimates on this blog, at – we calculate the total spill, at a very conservative estimate of 126,000 gallons (3,000 barrels) per day, was at least 9 million gallons.

  2. b.p. nichols says:

    This looks like solid, irrefutable work, so why is the Coast Guard still saying only 200,000 gallons per day are leaking out? The media is getting this story very wrong. I don't think the American public is prepared for how long this is going to last, and how bad this is going to be.

  3. John says:

    I think that you folks and McDonald have to consider that the aieral views only show the surface of a conical plume of oil. The conical plume begins one mile below the surface. It's shape is like an inverted mountain. To take the analogy further, you are looking at the base of the mountain, and estimating the size of the base, not the volume of the oil in the mountain. So, your estimate is off by quite a bit.

  4. John says:

    Thanks b.p. – it would help if Coast Guard would explain where their estimate is coming from. I have no way of knowing how they've come up with that figure.

  5. John says:

    John, thanks for the wonderful work. I have a bit of sorrow when saying that, because you worked to stop this. But I think going forward, you need to stop talking about this as a "spill." This event and the one in Australia have defined a new category of oil disaster. This is an oil well "rupture." Much like an artery rupture, it will beed until the pressure stops by a tourniquet or stops because there is no longer and pressure.

    You should also be careful to describe the plume vs. the visible "spill" on the surface. If I were you I would try to get an assessment of the plume. You need to shift the terms of this discussion to what it actually is rather than what it is not.

  6. Jay says:

    I cant imagine why the Government is covering up the amount of estimated daily leakage. Clearly, it took a big jump after 4/29, ( )

    Yes the Government, after NOAA says the leak was 5,000 bbls/day on 4/28, now is saying "It is impossible to estimate the amount of the leak" ( )
    Really. Why is that?
    I cannot imagine the reasons for holding back this information. Well, I can imagine — wild things like: The whole Gulf coast will have to be evacuated for months and they have not figured out how to do that.

  7. Arun says:

    I think that you folks and McDonald have to consider that the aieral views only show the surface of a conical plume of oil. The conical plume begins one mile below the surface. It's shape is like an inverted mountain. To take the analogy further, you are looking at the base of the mountain, and estimating the size of the base, not the volume of the oil in the mountain. So, your estimate is off by quite a bit.

    I rather disagree. The plume of oil does not encompass 2000 square miles at the surface, rather a small area (which can be estimated by the earliest size of the oil slick). The "base of the mountain" has been created by a lot of spreading by winds and ocean currents. This resembles a giant umbrella rather than an inverted mountain.

  8. PAL says:

    Thank you for this work. Interesting to hear your frustration about not having US radar satellite imagery. I worked for Oceana in 2002 and proposed using European SAR imagery to track oil spills around the world, given the apparent success of imaging illegal dumping by ships in the Mediterranean. Thought it might be useful for raising awareness, estimating oil spill damage, tracking spills in remote locations, and enforcement activities. Management wasn’t interested. Do you know of any regularly updated publically available radar imagery? As the spill spreads and disperses, it might help all of us better understand what’s happening.

  9. Evelyn Yvonne Theriault says:

    Just discovered your site as it is beginning to be referenced in the Canadian press.
    Why would Jay mention a situation where "the whole Gulf Coast will have to be evacuated for months"?
    Is there information somewhere about this possible scenario?
    Evelyn in Montreal

  10. Kenny says:

    Thanks John and skytruth for the first factual calculation attempts I have seen rather than a random number out of the air. It is time for the US government to come clean about what a disaster we have created for ourselves.

    Dennis in Asheville

  11. John says:

    Shape of plume: umbrella or mountain? I suspect that the shape is neither an umbrella or an inverted mountain, now. But as the oil disperses below the surface on its one-mile journey to the top, the ideal umbrella formation is probably going to become a conical structure with widening diameters at both the top and bottom. Also, it's quite conceivable that an underwater current is carrying some of the oil away, and we'll see a separate blotch on the surface in a few days. But the umbrella structure is the best-case assumption that assumes uniform properties for the oil and static properties for the mile journey underwater. It seems important to get a handle on what the rupture looks like from underwater.

  12. Christoph R says:

    Where are these overflight maps posted? I would think that the Coast Guard would have done another since April 28, but I can't find it online anywhere.

  13. Brooski says:

    There's been lots of interesting comments here, some even fairly intelligent ones actually, contrary to what you usually read in so many of the other blogs out there! But to discuss exactly what shape the plume has I think kind of misses the point of the information that the good FSU professor conservatively has provided us. Presumably in some kind of GIS, he measured simply the amount of oil that's actually floating on the surface, based on the segment area times the estimated average segment thickness, which is turn is based on reflectivity (color). There's most likely lots of other oil, between the water surface and the sandy bottom, that must be added to the total quantity, in order to get an even higher daily rate! As for the USCG making their initial assessment, and then later on a five times updated increase, it's because they and NOAA were (still are?) simply repeating what BP told them. Speaking of BP, it's sad that they are now trying to deflect the blame over to their drilling contractor who actually owns the semi-submersible, which is now sitting on the bottom of the Gulf. Sorry BP! Legally you are still liable, yeh you might be able to share the liability. But when it's all said and done, the drilling company probably will go belly up and you'll be stuck with the bulk of the recovery costs and federal fines. Of course, BP will simply pass on the costs to us drivers. Finally, why are they not deploying a manned underwater vehicle (MUV), such as NOAA's ALVIN, which is curently berthed at their research facility in Woods Hole, MA?

    Bruce H
    Fort Myers, FL

  14. mikedrabik says:

    So how much oil is out there today (05/03/10)?

    Do the math:

    One barrel = 42 gallons;

    26,000 barrels/per day =1,092,000 gallons;

    13 days = 14,1700,000 gallons!

    The question: why isn't the Media mentioning this? Why are they stuck on this figure of 5,000 barrels per day or saying it can't be estimated?

    This whole slick is hanging, like the sword of Damocles, over the Gulf Coast just waiting for the winds and currents to change to take it ashore.

    The odd thing is a lot people whom I've read who have have been interviewed by the Media and live there (and don't seem to be dependent on fishing or tourist industry for a living) seem to have taken an attitude that 'We need oil" and so this catastrophe is acceptable because the oil-based culture has to be preserved at all costs.

    So the Gulf covered in oil is acceptable? Tragic and delusional!

  15. Christoph R says:

    ….ok answered my own question. USCG District 8 posts the overflights on their flickr photostream. It looks like the most recent is the 29th, likely from the bad weather we've had down here over the weekend.

  16. Daysman says:

    The Gulf of Mexico is an awful lot larger than Prince William Sound, and it's currents are driven by the main Atlantic Ocean currents… and since this leak is 40 some miles out to sea, in deep water, and since the leak originates a mile deep, the whole Atlantic basin comes into play when figuring the dispersion of this slick. To watch the day to day push and pull on this oil is to realize that strong currents are acting upon it. Of course, BP is going to downplay the size of the leak, especially when they have strong natural dispersion acting on the slick… unless this oil is driven ashore in a strong way, they prefer to pretend it is not such a large leak – while mother nature hides the truth for them. They are also hitting this oil with chemical dispersants that will cause the oil to sink to the Gulf bottom… without ever surfacing. The truth is clawed out of statements about the blowout preventer… it did not function at all, so the only thing limiting the 150,000 barrels per day capacity of the well is the bent and mangled riser lying on the Gulf floor. To expect that somehow the pipe is magically holding back 97% of the deep well's high oil pressure in it's 800 foot torn section lying on the Gulf floor is ludicrous… oil is making it's way all the way out the end of that pipe. The good professor's estimate of 18% of oil pressure escaping from the riser sounds one heck of a lot more plausible and that is still a miracle of sorts.

    I agree with the post that calculated some 15 million gallons of oil has been released already, and all the attempts to capture this one million gallons per day are just as likely to create a much bigger leak (maybe MORE likely) as they are likely to succeed.

    All the while this slick grows it looms larger and larger as potential for landfall ANYWHERE in the Gulf, certainly anywhere on US coast. Right now, it looks quite plausible that before summer is done, this slick will make landfall EVERYWHERE the US touches the Gulf… and Cuba also.

  17. Yvette says:

    John, thank you for releasing your calculations. I first read them at oneEarth, and then saw your update at proPublica.

    Though this catastrophe has had media coverage it seems that for the epic disaster that it is most of the general public are taking this in stride. I could be wrong.

    My concern is unless we see oil soaked birds and fish kills in the news too many people will allow themselves to hoodwinked.

    The oil is going somewhere, and we have the additional concern with the dispersants that have been used. We'll all be paying a price for this mistake for many years to come.

  18. Mrs.B says:

    Wow, oh wow, I don't know what to say (through my shock and grief and concern) except 'thank you' Skytruth.

    Has anyone mentioned this well is brand-spanking-new into an untapped reservoir. Coast Guard Admiral Thad Allen gave a talk on May 5 to the New Orleans Times-Picayune and said BP officials were working on how much oil the reservoir would release until the pressure equalized. He said that's the only thing that will end this, that this disaster is 'indeterminate' unlike Katrina which had a beginning and an ending.

  19. John says:

    I received this comment via email on Saturday, May 8, 2010:

    Even BP's own (private) statements seem to lend credence to your numbers.

    "WASHINGTON In a closed-door briefing for members of Congress, a senior BP executive conceded Tuesday that the ruptured oil well in the Gulf of Mexico could conceivably spill as much as 60,000 barrels a day of oil, more than 10 times the estimate of the current flow." — NY Times

    Of course, BP is not actually saying that the 60,000 barrels per day is the current leak rate, but they are at least indicating what is POSSIBLE from the well in question — presumably with an uncontrolled flow.

    And, of course, though 60,000 barrels per day is about twice your own minimum estimate based on the image analysis, it is the same order of magnitude as what you guys have estimated — and an order of magnitude greater than the "official" number that all the news media keep quoting.

    After looking at the data myself, I think the '5000 barrels per day" is highly suspect, not least of all because no one has even said what it is based on (the statement of a PR flak at BP or in the Obama adminstration?)

    Anyway. Keep up the great work.

    It's good someone actually cares about the truth, even if our "leaders" and fawning corporate media apparently don't (seem intent on actually hiding it, in fact)

    L Jewett

  20. Saugertlog says:

    The media brouhaha about the slick has completely ignored the harsher reality of the undersea migration of the oil which, by now, must be clear onto the other side of Florida – yes, well past the Keys and the Everglades – and already into the Atlantic… and as for the aquifers that supply water to Florida… I wonder how long that'll be potable. Sad, tragic, criminal all of this.

  21. Bob O Bob says:

    Undersea Migration?? Is it alive/ What a croc.

    Interesting but totally off the mark. I am an environmental scientist right here right now in the Gulf and if anything the flow is less than they predicted, for whatever reason. You can always find an expert or two to blow thing out of proportion, especially if they are trying to toot their own research. Npr should know better. The USCG, NOAA and everone else is doing everything they can to accurately report this stuff and they have lots of scientist and years of research behind what they are doing.

    The facts are: The slick is 40% smaller today than it was last week due to the skimming, dispersion, and in-situ burning than it was last week. We are finding very few oiled bird, almost absurdly low, considering the number of people we have down here. So somehow they (BP) is actually managing thru herculean effort to pick up disperse or burn up more oil than is being discharged, and they are not picking up that much. So there can't be that much more than the estimates.

    I personally believe the oil is less toxic than expected, less resistant to microbial degradation or whatever and so it is not as big a deal as first thought. I am very glad of that and very glad that BP has mobilized all the response that it has.

  22. Tony says:

    A thought. Obviously, the Horizon spill was the result of a series of, to be very kind to all involved, inappropriate behaviors and reckless actions by many. However, my observation and question is somewhat different. If, at a minimum, the Horizon spill is continuing to leak 26,500 BARRELS of oil PER DAY, and there are in excess of 1,300 oil oil producing wells in the Gulf of Mexico alone, and each well is capable of producing only one-half [13,000 barrels per day] of the production of the oil coming from the Horizon blow-out, then why we do we have shortages of oil and need more wells in the first place? 13,000 x 1,300 is approximately 16,900,000 BARRELS of oil per day that can be can be produced in the Gulf ALONE right now. And, as I understand the matter, the Horizon well was beng 'capped' for future use.

    The Gulf numbers absolutely ignore the rest of the world. Has anyone hought that while we certainly need to be taking action now to stop the uncontrolled Horizon flow,the larger question is the amount of oil we have available to us in the U.S. right now, but apparently are not bringing to market? I have heard no one discuss the matter and do not understand why. I certainly do not understand total world demand but believe it to be about 85 Million barrels per day. If remotely true, we need to look at the numbers. Something is amiss. The oil in the Gulf from existing wells is a very small amount of the total oil that can be produced across the world. And it does not even count natual gas availability. It seems to me the debate, the questions, the investigations, and we the people need to ask the larger questions – and demand honest answers. Hopefully, those of you who are more involved and much smarter than me will think about my questions. Even if remotely correct, maybe the Horizon disaster also provides all of us the unique opportunity to demand answers to the simplest [but likely, the most important and guarded] of questions and answers. What is really occurring that has caused an energy 'crisis' that requires us to take such huge risks for addtional oil wells, like Horizon, that are being drilled and then capped. I personally believe in drilling and creating new energy sources, but I also believe in the truth. And the truth seems to be elusive in the case of true oil reserves, availability and needs.

  23. Michael says:

    Yes there is definitely something going on with a concealment of real facts and information about this disaster. Why? Because maybe something larger and unforseen is being hidden. I'm not saying this is a conspiracy theory, but so many things don't add up and there are too many inconsistencies with data we are seeing. Not to mention, that riser line should have been capped by now… if all the most brilliant minds are working on it, 5 out of 5 projects to try and stop the "leak" wouldn't have failed. If this deep water drilling is such new territory, there would have been LOADS of research done before anything actually went into production. If not, it was a poorly managed project to begin with.

  24. EntertainmentNews says:

    What should be investigated is BP's initial surveyance of the amount of oil contained in the reservoir of oil 3 1/2 miles down, which inspired them to believe there were considerable profits to go to the extreme of drilling so far down. Is this reservoir so deep that it is connected to other reservoirs of oil that could keep this going until the oceans are overwhelmed?

  25. TJ says:

    Think the Gulf situation is bad now, wait until BP does an Exxon and fights all the fines, penalties and claims in court. Exxon got away with paying very little for the Valdez spill thanks to the courts, especially the Supreme Court. No doubt BP will take the same path. They display sadness and remorse because that is what is expected. The real intentions of BP will play out in the months and years to come.

  26. Tavi says:

    The Exxon Valdez and BP Horizon oil spills shows that accidents happen.

    If Enbridge’s Northern Gateway pipeline project is approved it would carry half a million barrels of crude oil a day from the Alberta tar sands to the port of Kitimat, B.C. The oil would then be loaded into tankers that would sail through the narrow inlets of the Great Bear Rainforest before heading out to sea. At least 225 oil tankers a year would traverse this fragile coastal route, delivering tar sands oil to Asian markets.

    Stop the Enbridge Pipeline. E-mail the Prime Minister and urge him to permanently ban super tankers so that B.C.’s North and Central Coast is not the site of the world’s next disastrous oil spill.

    Action alert link in video:

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