Originally Released October 6, 2010

Updated January 11, 2011

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National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling

THE USE OF SURFACE AND SUBSEA DISPERSANTS DURING THE

BP DEEPWATER HORIZON OIL SPILL

Staff Working Paper No. 4

Staff working papers are written by the staff of the National Commission on the BP Deepwater 

Horizon Oil Spill and Offshore Drilling for the use of members of the Commission. They do not 

necessarily reflect the views of the Commission or any of its members. In addition, they may be 

based in part on confidential interviews with government and non-government personnel.

This working paper examines the issues raised by the use of dispersants in the Deepwater 

Horizon spill. Dispersants change the distribution, not the amount, of oil within a marine 

environment. They are chemicals typically applied directly to oil on the water surface in order to 

break the oil into small droplets that can then mix with water below the surface. The dispersed 

oil is rapidly diluted, mixing both vertically and horizontally in the water column.1 While this 

alleviates high concentrations at the surface, it may expose organisms to lower, but more 

widespread, concentrations of oil.

The use of dispersants in the aftermath of the Macondo deepwater well explosion was 

controversial for three reasons.2 First, the total amount of dispersants used was unprecedented: 

1.84 million gallons. Second, 771,000 of those gallons were applied at the wellhead, located 

5,067 feet below the surface. Little or no prior testing had been done on the effectiveness and 

potential adverse environmental consequences of subsea dispersant use, let alone at those 

volumes.3 Third, the existing federal regulatory system pre-authorized dispersant use in the Gulf 

 

1

Press Conference with Lisa P. Jackson, EPA Administrator (May 24, 2010), available at http://www.epa. 

gov/bpspill/dispersants/statement-dispersant-use-may24.pdf [hereinafter Jackson Press Conference]. For further 

information about dispersants, see Committee on Understanding Oil Spill Dispersants: Efficacy and Effects, 

National Research Council of the National Academies, UNDERSTANDING OIL SPILL DISPERSANTS: EFFICACY AND 

EFFECTS 9 (2005), available at http://www.nap.edu/catalog/11283.html [hereinafter NRC Report].

2 The day after the Macondo well was capped and the amount of daily dispersant use dropped precipitously, a group 

of marine scientists opposed to the high volume use of dispersants issued a statement calling for an immediate end to 

their use. See Susan D. Shaw et al., Consensus Statement: Scientists Oppose the Use of Dispersant Chemicals in 

the Gulf of Mexico (July 16, 2010), available at 

http://www.meriresearch.org/Portals/0/Documents/CONSENSUS%20STATEMENT%20ON%20DISPERSANTS%

20IN%20THE%20GULF%20updated%20July%2017.pdf.

3 BP’s ―Lessons Learned‖ report refers to ―limited trials‖ and ―some discussion in technical papers of applying 

dispersant to the source.‖ BP, DEEPWATER HORIZON CONTAINMENT AND RESPONSE: HARNESSING CAPABILITIES 

AND LESSONS LEARNED 26 (2010), available at http://www.boemre.gov/ooc/PDFs/NarrativeFinal.pdf. BP also 

claims that ―EPA has permitted use of dispersants subsea to remediate oil spills since the 1990s.‖ Id. None of the 

experts (whether from EPA, from BP, or independent) with whom Commission staff spoke in researching this paper 

was aware of prior subsea use of dispersants, which suggests that any such use or approval was not well-known. On 

September 7, 2010, we requested information from BP’s counsel regarding the trials, papers, and EPA actions to 

which BP refers. On September 27, 2010, BP’s counsel confirmed in an email to Commission staff that ―the 

reference on page 26 of the report to EPA’s approval of subsea dispersant use in the 1990s is an error. Although 

dispersants have been on the Product Schedule since the 1970s, we understand that only surface uses were 

contemplated in the 1990s.‖ BP’s counsel also provided the Commission staff with references to two technical 

papers discussing the application of subsea dispersants. See, e.g., NRC Report at 138. 
Originally Released October 6, 2010

Updated January 11, 2011

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of Mexico without any limits or guidelines as to amounts or duration. Faced with an emergency, 

the government had to make decisions about high-volume and subsea dispersant use within time

frames that denied officials the opportunity to gather necessary information. The resulting 

uncertainty even fueled unfounded suspicions that BP was using dispersants without 

authorization from the government in an effort to mask the oil and to limit its ultimate liability.

This paper considers two issues. The first is how well the government handled the 

dispersant issues it faced in the absence of necessary scientific information and pursuant to a 

regulatory regime that had failed to anticipate this kind of problem. The second is how, in light 

of lessons learned from this recent experience, government procedures and existing laws might 

be improved to allow for sounder decisions regarding the use of dispersants in the future. 

The paper is divided into three parts. Part I provides background information on 

dispersants and their potential authorization for use in responses to oil spills. It then recaps the 

chronology of the use of dispersants following the Macondo well explosion. This chronology 

includes the volume of dispersants used, where they were used, the types of dispersants used, and 

the role of various government agencies in making relevant decisions regarding dispersant use. 

Part I also describes some of the contemporaneous public controversy concerning the use of 

dispersants, including the debate, still ongoing, regarding their potentially adverse impacts. Part 

II considers the distinct questions of whether the government’s decisions were reasonable at the 

time; and whether, regardless of their reasonableness or unreasonableness when made, 

preliminary scientific research since undertaken suggests those decisions may, in fact, have been 

sensible. Finally, Part III describes some possible implications for changes in agency procedures 

and regulations arising out of the use of dispersants in the Deepwater Horizon spill response that 

Commissioners may wish to consider.

I. Background on Dispersants

A. The Trade-offs of Dispersant Use

When an oil spill occurs, responders have several tools to manage potential 

environmental impacts. Mechanical means are generally preferred, but they cannot always be 

used and do not recover all of the spilled oil.4 Non-mechanical methods such as in-situ burning 

and chemical dispersants can contribute to the elimination or breakdown of the oil. In response 

to the Deepwater Horizon oil spill, BP used large amounts of the dispersant Corexit 9500 and 

some Corexit 9527.5

Dispersants function like detergents to break up oil into small droplets that mix easily 

with water. They contain a combination of surfactants and solvents. Surfactants are compounds 

that have lipophilic groups, which mix with non-polar substances like oil, and hydrophilic 

 

4

See NRC Report at 9 (―The effectiveness of mechanical response techniques is variable and highly influenced by 

the size, nature, and location of the spill as well the environmental conditions under which the response is carried 

out. Essentially, mechanical response works satisfactorily under a finite subset of all possible spill scenarios.‖).

5

See David Biello, Is Using Dispersants on the BP Gulf Oil Spill Fighting Pollution with Pollution?, SCI. AM. (June 

18, 2010), available at http://www.scientificamerican.com/article.cfm?id=is-using-dispersants-fighting-pollutionwith-pollution. Toxicity information on these dispersants can be found in Anita George-Ares & James R. Clark, 

Aquatic Toxicity of Two Corexit Dispersants, 40 CHEMOSPHERE 897 (2000).
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Updated January 11, 2011

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groups, which mix with polar substances like water. By combining lipophilic and hydrophilic 

groups, surfactants can lower surface tension to allow water and oil to mix more easily.6 The 

solvents help the surfactants pass through the oil to reach the oil-water boundary where the 

surfactants operate.7

The resulting oil/water mixture takes the form of small droplets of dispersant-covered oil, 

which, because of their small size, can remain suspended in water rather than rising to the 

surface.8 These droplets can move into and through the water column from the water’s surface.9 

This process depends on outside forces to disperse the oil droplets through the top of the water 

column. For that reason, dispersants applied to surface oil slicks are more effective in areas with 

high wave energy.10

The toxicity of available dispersants has diminished substantially over the past several 

decades.11 Generally, dispersants are less toxic than oil. Chemically dispersed oil, however, can 

be toxic in both the short and long term, and less oil on the surface means more elsewhere in the 

water, spread over a wider area.

Using dispersants to remove oil from the water surface has several potential benefits. 

First, less oil will float ashore to adversely affect shorelines and fragile estuarine environments. 

Second, animals and birds that float on or wade through the water surface may be less exposed to 

oil.12 Third, dispersants may accelerate the rate at which oil biodegrades. Smaller droplets have 

a larger surface-area-to-volume ratio, which in theory should allow microorganisms greater 

access to the oil, and speed their rate of consumption. The expected acceleration of this 

biodegradation is often cited as a major reason to use dispersants. 

There are uncertainties regarding both the actual realization of some of these benefits, 

especially in the subsea, and potential offsetting costs. For instance, less oil on the surface 

means more in the water column, increasing exposure for subsurface marine life. And, while the 

smaller droplets may accelerate biodegradation, their smaller size increases the dissolution of 

potentially toxic compounds and exposure to aquatic organisms. Moreover, according to at least 

some scientific literature, the assumption of increased biodegradation may not always be 

accurate. Some studies have found that dispersants have no effect on the biodegradation rate or 

may even inhibit biodegradation.13 It is also only largely in the aftermath of the Macondo well 

explosion that scientists have begun to research the extent to which oil-eating bacteria are present 

 

6

See Coastal Response Research Center, RESEARCH & DEVELOPMENT NEEDS FOR MAKING DECISIONS REGARDING 

DISPERSING OIL 1 (Apr. 2006), http://www.crrc.unh.edu/dwg/dispersant_workshop_report-final.pdf [hereinafter 

CRRC Report]. 

7

See International Tanker Owners Pollution Federation Ltd, Dispersants, http://www.itopf.com/spillresponse/clean-up-and-response/dispersants/.

8

See CRRC Report at 7.

9

See NRC Report at 10.

10 See Merv Fingas, A REVIEW OF LITERATURE RELATED TO OIL SPILL DISPERSANTS 1997-2008 5 (Sept. 2008), 

available at http://www.pwsrcac.org/docs/d0053000.pdf. 

11 NRC Report at 207.

12 The NRC Report, however, suggests that the effect of dispersants on the fur and feathers of animals and birds—

e.g., potential negative effects on waterproofing—requires further study. See NRC Report at 196, 274.

13 See Fingas at 22.
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Updated January 11, 2011

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at the low temperatures of deepwater.14 Finally, there is no reason to suppose that all dispersants 

act in the same manner. They may, depending upon their chemical makeup, have strikingly 

dissimilar impacts. For example, some evidence indicates that the ionic surfactant in Corexit 

9527 and 9500 inhibits biodegradation while their non-ionic surfactants increase 

biodegradation.15

B. Regulation of the Use of Dispersants in Oil Spill Response

The Clean Water Act expressly contemplates the use of dispersants in response to oil 

spills. Section 311(d)(2)(G) of the Act requires that the federal National Contingency Plan for 

oil spill response contain a schedule identifying:

(i) dispersants . . . , if any, that may be used in carrying out the Plan,

(ii) the waters in which such dispersants . . . may be used, and

(iii) the quantities of such dispersant . . . which can be used safely in such waters . . . .

16

In addition, subsection (G) requires each schedule to provide for use of other, non-listed 

dispersants: ―[T]he President, or his delegate, may, on a case-by-case basis, identify the 

dispersants, other chemicals, and other spill mitigating devices and substances which may be 

used, the waters in which they may be used, and the quantities which can be used safely in such 

waters.‖17

The National Contingency Plan under the Clean Water Act and Oil Pollution Act of 1990 

further provides for the establishment of regional and area-wide contingency plans, which may 

expressly pre-authorize the use of dispersants:

In meeting the provisions of this paragraph, preauthorization plans may address factors 

such as the potential sources and types of oil that might be spilled, the existence and 

location of environmentally sensitive resources that might be impacted by spilled oil, 

available product and storage locations, available equipment and adequately trained 

operators, and the available means to monitor product application and effectiveness . . . . 

Approved preauthorization plans shall be included in the appropriate RCPs and ACPs 

[regional and area contingency plans].18

When dispersants have not been pre-authorized in an oil spill response contingency plan, 

they can still be approved after a spill has occurred. Federal regulations require the Federal OnScene Coordinator to obtain ―concurrence‖ in this circumstance from EPA and applicable state 

authorities, but require only ―consultation‖ with the Department of Commerce (through the 

National Oceanic and Atmospheric Administration [NOAA]) and the Department of the Interior:

 

14 See, e.g., Richard Camilli et al., Tracking Hydrocarbon Plume Transport and Biodegradation at Deepwater 

Horizon, SCIENCE (Aug. 19, 2010) , http://www.sciencemag.org/cgi/content/abstract/science.1195223; Terry C. 

Hazen et al., Deep-Sea Plume Enriches Indigenous Oil-Degrading Bacteria, SCIENCE (Aug. 24, 2010), 

http://www.sciencemag.org/cgi/content/abstract/science.1195979. 

15 See Fingas at 22. 

16 33 U.S.C. § 311(d)(2)(G).

17 Id. 

18 40 C.F.R. § 300.910(a).
Originally Released October 6, 2010

Updated January 11, 2011

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[T]he OSC [On-Scene Coordinator], with the concurrence of the EPA representative to 

the RRT [Regional Response Team] and, as appropriate, the concurrence of the RRT 

representatives from the states with jurisdiction over the navigable waters threatened by 

the release or discharge, and in consultation with the DOC [Department of Commerce, 

i.e., NOAA] and DOI [Department of the Interior] natural resource trustees, when 

practicable, may authorize the use of dispersants, surface washing agents, surface 

collecting agents, bioremediation agents, or miscellaneous oil spill control agents on the 

oil discharge, provided that the products are listed on the NCP [National Contingency 

Plan] Product Schedule.19

The effect of pre-approval, accordingly, is to eliminate the need for approvals and consultations

during the response and to enable the Federal On-Scene Coordinator to act without delay.

The National Contingency Plan also establishes ―Area Committees‖20 under the direction 

of a Federal On-Scene Coordinator21 that are charged with ―work[ing] with State and local 

officials to expedite decisions for the use of dispersants and other mitigating substances and 

devices.‖22

The decision whether to approve the use of dispersants can be difficult, whether it occurs

through the pre-approval process in developing a contingency plan or, in the absence of preapproval, once a spill has occurred. As described by the National Research Council of the 

National Academies of Sciences, ―[g]iven the potential impacts that dispersed oil may have on 

water-column and seafloor biota and habitats, thoughtful analysis is required prior to the spill 

event so that decision makers understand the potential impacts with and without dispersant 

application.‖23 The trade-offs are complex:

Decisions to use dispersants . . . involve trade-offs between decreasing the risk to water 

surface and shoreline habitats while increasing the potential risk to organisms in the 

water column and on the seafloor. This trade-off reflects the complex interplay of many 

variables, including the type of oil spilled, the volume of the oil, sea state and weather, 

water depth, degree of turbulence (thus mixing and dilution of the oil), and relative 

abundance and life stages of resident organisms.24

 

19 40 C.F.R. § 300.910(b). 

20 ―There is established for each area designated by the President an Area Committee comprised of members 

appointed by the President from qualified personnel of Federal, State, and local agencies.‖ Clean Water Act 

§ 311(j)(4)(A); 40 C.F.R. § 300.5. In the spill-affected area there are two ―areas‖ (and thus Area Committees) for 

Louisiana, three for Texas, two for Northwest/West Florida, and one for Mississippi/Alabama.

21 ―On-scene coordinator (OSC) means the federal official pre-designated by EPA or the USCG [U.S. Coast Guard] 

to coordinate and direct responses under subpart D, or the government official designated by the lead agency to 

coordinate and direct removal actions under subpart E of the NCP.‖ 40 C.F.R. § 300.5. Rear Admiral Mary Landry 

was the Federal On-Scene Coordinator until June 1, 2010, when Rear Admiral James Watson assumed that role. On 

July 12, 2010, Rear Admiral Paul Zukunft replaced Admiral Watson as the Federal On-Scene Coordinator.

22 Clean Water Act § 311(j)(4)(B); see also 40 C.F.R. § 300.910(a) (―RRTs Area Committees shall address, as part 

of their planning activities, the desirability of using appropriate dispersants, surface washing agents, surface 

collecting agents, bioremediation agents, or miscellaneous oil spill control agents listed on the NCP Product 

Schedule, and the desirability of using appropriate burning agents.‖).

23 See NRC Report at 3. 

24 Id. at 2.
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Under the National Contingency Plan, EPA is responsible for obtaining dispersant 

toxicity data from industry before placing a dispersant on the product schedule, which then 

serves as the basis for listing particular dispersants for pre-approved use in oil spill response 

contingency plans. The accuracy and consistency of pre-listing testing by manufacturers has 

been questioned, with toxicologists suggesting that the results of industry testing vary more 

widely than they should.25

Moreover, the required pre-authorization testing is limited to acute toxicity studies (48 

and 96 hours) on two species: a fish species and a mysid shrimp species, Menidia beryllina and 

Mysidopsis bahia, respectively. EPA commonly uses these species in laboratory tests, and they 

are useful in providing comparative acute toxicity information, but the tests are not designed as 

proxies for all possible adverse ecosystem impacts. The pre-testing of dispersants did not 

include other important matters such as environmental persistence, effectiveness with multiple 

varieties of oil and at multiple temperatures, byproducts, and endocrine effects. 

C. The Use of Dispersants in Response to the Deepwater Horizon Spill26

The federal government’s response to the oil spill began immediately after the Macondo 

well explosion on the night of April 20, 2010. In addition to the emergency search-and-rescue 

mission, efforts to address the released oil were soon underway. Pursuant to the National 

Contingency Plan, the Coast Guard Captain of the nearest port, Morgan City, Louisiana, served 

as the Federal On-Scene Coordinator, in charge of the government’s response action, until a few 

days later when the District (Eight) Commander, Rear Admiral Mary Landry, took over the 

Coordinator role. 

The oil spill response contingency plans applicable to the Gulf (Regions 4 and 6 within 

the National Response Plan framework) pre-authorized the use of a list of specific dispersants. 

Neither of the plans limited the overall volume or duration of such pre-authorized use.27 With 

 

25 See Biello, Fighting Pollution with Pollution. Discrepancies between the pre-approval tests and EPA’s post-spill 

toxicity testing results suggest that there were potential flaws in the earlier testing, although it may not be possible to 

resolve that question definitively at this late date. The pre-approval tests found differences in toxicity between 

dispersants that did not appear in the EPA test. Gulf Coast Oil Spill: Small Business and the Cleanup Effort Before 

the S. Subcomm. On Small Business and Entrepreneurship, 111th Cong. (June 18, 2010) (statement of Carys 

Mitchelmore) (―Noteworthy is that the reference toxicant LC50s for the different dispersants listed on the NCPPS 

differ by orders of magnitude, up to nearly 300-fold. For example, in Table 2 reference toxicant data for the mysid 

shrimp tests range from an LC50 (ppm, 96-hr) from 0.98 (for Sea Brat #4) to 267.7 (for Nokomis 3-F4). One 

product (Nokomis 3-AA) used copper sulfate as a reference toxicant instead of the EPA-required SDS reference 

toxicant. These issues are of concern if you are trying to compare the relative toxicity of the dispersants. Indeed, 

this currently, cannot be accurately assessed given the data presented on the NCPPS. These toxicity tests should be 

repeated.‖).

26 The working relationship between the Coast Guard and EPA with respect to dispersant-related decisions during 

the spill is discussed more fully in the Commission’s final report.

27 The Region 6 dispersant guidelines pre-authorize use of any dispersant on the National Product Schedule in water 

at least ten meters deep and at least three miles from shore. Region 4’s dispersant guidelines give the same general 

pre-authorization, but exclude certain geographic areas. Both sets of guidelines also provide the Federal On-Scene 

Coordinator with a checklist of factors to consider—not including overall volume or duration —in determining 

whether to permit dispersant use. RRT-6, FOSC DISPERSANT PRE-APPROVAL GUIDELINES AND CHECKLIST (2001), 

available at http://www.losco.state.la.us/pdf_docs/RRT6_Dispersant_Preapproval_2001.pdf; REGION IV REGIONAL 

RESPONSE TEAM RESPONSE AND TECHNOLOGY COMMITTEE DISPERSANT WORKGROUP, USE OF DISPERSANTS IN 
Originally Released October 6, 2010

Updated January 11, 2011

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the permission of the Federal On-Scene Coordinator, BP applied 14,654 gallons of the dispersant 

Corexit, which was on the approved list, on the surface during the week of April 20-26, 2010.28 

On April 29, 2010, the Coast Guard formally designated the Gulf spill a ―Spill of National 

Significance‖ pursuant to the Oil Pollution Act.

29

 Based on that designation, the Commandant of 

the Coast Guard, Admiral Thad Allen, became the ―National Incident Commander‖ in charge of 

coordinating interagency efforts on the wide variety of issues responders faced, and dealing with 

high-level political and media inquiries related to the response. 

During May, dispersants were applied both to the surface and subsea, and the volume 

used increased rapidly. During the week of April 27 to May 3, 2010, responders applied 141,358 

gallons to the surface, and that amount grew to 168,988 by the following week.30 The week of 

May 11 to May 17, 2010, the amount of surface dispersants used reached 255,000 gallons.31

On May 1, 2010, Admiral Thad Allen reported that response crews had begun testing the 

subsurface application of dispersants to oil escaping from the broken riser.

32

 Nearly 3,000 

gallons of subsea dispersants were applied.33 At the time, it was unclear whether the National 

Contingency Plan’s pre-approval of the use of dispersants in the Gulf applied to subsea use in 

addition to surface use, and therefore whether additional EPA approval and NOAA consultation 

were required.34 Notwithstanding those uncertainties regarding governing law, on May 7, 2010,

―having deployed test applications of subsea dispersants, EPA halted subsea dispersant 

operations, awaiting additional test results.‖35

Testing and monitoring, however, presented substantial logistical and organizational 

problems. BP itself performed three tests, based on protocols established by EPA and the Coast 

Guard.36 On May 15, 2010, the testing for effectiveness and toxicity that had been completed

prompted EPA and the Coast Guard to announce their joint approval of subsea dispersant use 

 

REGION IV (1996), available at

http://ocean.floridamarine.org/acp/mobacp/PDF/ANNEXES/RRT%20IV%20Dispersant%20Policy.pdf. 

28 Figures on the volume of dispersant use are either taken directly from, or calculated based on data in, the 

Operations and Ongoing Response daily reports for the Deepwater Horizon Response, available at 

www.restorethegulf.gov [hereinafter Restore the Gulf Estimates]. 

29 Campbell Robertson, White House Takes a Bigger Role in the Oil Spill Cleanup, N.Y. TIMES (Apr. 29, 2009).

30 Restore the Gulf Estimates. 

31 Id. 

32 See Transcript from Press Briefing, Coast Guard Commandant Thad Allen and Assistant to the President for 

Homeland Security John Brennan (May 1, 2010), available at http://coastguardnews.com/gulf-oil-spill-pressconference-transcript/2010/05/01/; Deepwater Horizon Response, The Ongoing Administration-Wide Response to 

the Deepwater Horizon Oil Spill (May 3, 2010), available at 

http://www.restorethegulf.gov/release/2010/05/03/ongoing-administration-wide-response-deepwater-horizon-oilspill [hereinafter May 3, 2010 Release]. 

33 May 3, 2010 Release. 

34

 Interview with Coast Guard official.

35 See H.R. Committee on Energy and Commerce, 111th Cong., CHRONOLOGY OF DEEPWATER HORIZON EVENTS, 

available at http://energycommerce.house.gov/documents/20100615/EE.Attachment.A.2010.6.12.pdf.

36 See Conference Call with Lisa P. Jackson, EPA Administrator (May 12, 2010), available at

http://www.epa.gov/bpspill/dispersants/may12transcript-final.pdf; see also Joel Achenbach & Steven Mufson, 

Engineers draw battle lines in effort to plug gulf oil well: ‘Top hat,’ ‘hot tap’ among tactics pursued; uncertainties 

still loom, WASH. POST (May 11, 2010). 
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with the condition that BP conduct further monitoring.

37

 The EPA Administrator, Lisa Jackson, 

made the approval decision on behalf of EPA herself and has since publicly acknowledged the 

difficulty of making this decision with the limited amount of scientific information then 

available. Considerations related to response worker health and ease of application—subsea 

application would minimize the necessary human contact with dispersants, and could occur at 

night and in foul weather—reportedly played a role in the decision to approve the method.

38 By 

May 17, 2010, BP had made extensive use of dispersants. The cumulative totals by this time 

were 580,000 gallons on the surface and 45,000 gallons subsea. 

On May 20, 2010, in the wake of continuing media reports relating public concern about 

the potential toxicity of the high volumes of dispersants being used,

39 the Coast Guard and EPA 

issued a joint directive requiring BP to identify and use a less toxic and more effective dispersant 

than Corexit 9500 from the list of dispersants authorized by the National Contingency Plan.

40

 

According to the data in the National Contingency Plan Product Schedule, some of the preapproved dispersants were both less toxic and more effective on South Louisiana crude oil than 

Corexit 9500.

41 Based on the Plan, the federal directive required BP to identify a less toxic 

alternative to be used both on the surface and subsea at the source of the oil leak within 24 hours, 

and to begin using the less toxic dispersant within 72 hours of submitting the alternative. 

Specifically, the directive called for toxicity levels LD50 ―at or below‖ 23 parts per million (ppm) 

for Menidia or 18 ppm for Mysidopsis.

42 If BP was unable to identify acceptable alternative 

dispersant products, BP had to provide the Coast Guard and EPA with a detailed description of 

 

37 See EPA, DISPERSANT MONITORING AND ASSESSMENT DIRECTIVE FOR SUBSURFACE DISPERSANT APPLICATION

(May 10, 2010); available at http://www.epa.gov/bpspill/dispersants/subsurface-dispersant-directive-final.pdf ; 

EPA, DISPERSANT MONITORING AND ASSESSMENT DIRECTIVE FOR SUBSURFACE DISPERSANT APPLICATION–

ADDENDUM 1 (May 14, 2010), available at http://www.epa.gov/bpspill/dispersants/subsurface-dispersantaddendum-final.pdf; Press Release, Deepwater Horizon Incident Joint Information Center, Coast Guard and EPA 

Approve Use of Dispersant Subsea in Further Effort to Prevent Oil From Reaching U.S. Shoreline (May 15, 2010), 

available at http://www.restorethegulf.gov/release/2010/05/15/coast-guard-and-eps-approve-use-dispersant-subseafurther-effort-prevent-oil-reac.

38 Jeff Goodell, The Poisoning, ROLLING STONE (July 21, 2010). Administrator Jackson gave a wide-ranging and 

candid interview to Rolling Stone, in which she stated that she had told her aides that the approval decision was 

among the hardest she had ever made. She also reportedly said that BP argued for subsea application as a method 

that would reduce the overall volume of chemicals discharged into the marine ecosystem. Id.

39 See, e.g., Elizabeth Rosenthal, In Gulf of Mexico, A Huge Experiment with Chemical Dispersants, N.Y. TIMES

(May 6, 2010) (characterizing ―BP and federal officials [as] engaging in one of the largest and most aggressive 

experiments with chemical dispersants in the history of the country, and perhaps the world.‖).

40 See EPA, DISPERSANT MONITORING AND ASSESSMENT DIRECTIVE FOR SUBSURFACE DISPERSANT APPLICATION–

ADDENDUM 2 (May 20, 2010), available at http://www.epa.gov/bpspill/dispersants/directive-addendum2.pdf 

[hereinafter EPA ADDENDUM 2]. BP had used Corexit 9500 and 9527, though it discontinued use of the latter early 

on during the spill because Corexit 9527 contained 2-butoxyethanol, which had allegedly created health problems 

for Exxon Valdez workers. See Elana Schor, Ingredients of Controversial Dispersants Used on Gulf Spill Are Secret 

No More, N.Y. TIMES (June 9, 2010).

41 See EPA, NATIONAL CONTINGENCY PLAN PRODUCT SCHEDULE TOXICITY AND EFFECTIVENESS SUMMARIES, 

available at http://www.epa.gov/emergencies/content/ncp/tox_tables.htm#dispersants.

42 See EPA ADDENDUM 2. LD50 is the dose that is lethal to 50% of the test population. Menidia is a genus of 

silverside fish found in the Gulf of Mexico. Mysodopsis are a type of shrimp used for toxicity testing. The reference 

to toxicity levels ―at or below‖ designated LD50 levels was confusing, because a higher LD50 actually means a safer 

substance. 
Originally Released October 6, 2010

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the alternative dispersants investigated, and the reasons it believed those products did not meet 

the required standards.43

BP responded to the directive the day it was issued.

44 BP contended that only five 

products on the National Contingency Plan Product Schedule (which lists acceptable dispersants) 

met the criteria in the directive and that Corexit 9500A was the ―best alternative.‖45 BP noted 

that one of these five acceptable dispersants ―contains a small amount of a chemical that may 

degrade to a nonylphenol,‖ a class of chemicals that have been identified as potential endocrine 

disruptors and may persist in the environment for a period of years.46 Unfortunately, BP said, 

neither the manufacturer nor BP had had the opportunity to test the product for these potential 

effects.47

BP said that it would be prudent to obtain the chemical formulas for the other dispersants 

to evaluate their potential to degrade to a nonylphenol, but indicated that it had not been able to 

do so.

48 BP noted that ―there may be only limited information on the constituents of the 

dispersants, since the dispersants typically contain proprietary substances whose identities are 

not publicly available.‖49 In contrast, BP explained, the manufacturer of Corexit had said that it 

reached ―maximum biodegradability‖ within one month and was not persistent in the 

environment.50 In short, BP concluded, Corexit ―appears to have fewer long term effects than 

the other dispersants evaluated.‖51 BP also made clear that the company did not, in any event, 

then have a sufficient stockpile of any dispersants other than Corexit and Sea Brat #4, and that 

the Sea Brat #4 supply might not be sufficient for both surface and subsea use.52 Corexit 9500 

was the only dispersant used during the remainder of the spill.

In a May 24, 2010 press conference, EPA Administrator Jackson stressed three points, 

while generally acknowledging that federal regulators remained ―deeply concerned about the 

things we don’t know‖ such as the ―long-term effect on aquatic life.‖

53 First, she said, the 

government was instructing BP to ―take immediate steps to significantly scale back the overall 

 

43 See id. 

44 See Letter from Douglas J. Suttles of BP to Rear Admiral Mary Landry, Commander, Eighth Coast Guard 

District, and Samuel Coleman, Director, Superfund Division EPA Region 6 (May 20, 2010), available at

http://www.epa.gov/bpspill/dispersants/5-21bp-response.pdf [hereinafter Suttles Letter]. This letter refers to the 

directive (EPA Addendum 2) as having a May 19, 2010 date.

45 Corexit is a product of the Nalco Company, headquartered in Napier, Illinois. Corexit 9500A contains petroleum 

distillates, propylene glycol, and a proprietary organic sulfonate (a type of detergent). See Safety Data Sheet, Nalco 

Company, Corexit EC 9527A (May 11, 2010), available at

http://www.restorethegulf.gov/sites/default/files/imported_pdfs/external/content/document/2931/539295/1/Corexit%

20EC9527A%20MSDS.pdf.

46 See Suttles Letter. 

47 See id. The manufacturer tests were also conducted by different laboratories and on dispersants mixed with No. 2 

fuel oil, not Louisiana sweet crude. See EPA, DISPERSANTS TOXICITY TESTING–PHASE II QUESTIONS AND ANSWERS

(Aug. 2, 2010), available at http://www.epa.gov/BPSpill/dispersants/qanda-phase2.pdf [hereinafter DISPERSANTS 

TOXICITY Q&A] (explaining in answer to question seven that No. 2 fuel oil is not the oil in the Gulf).

48 See Suttles Letter.

49 Id.

50 Id. 

51 Id.

52 See id. 

53 Jackson Press Conference.
Originally Released October 6, 2010

Updated January 11, 2011

- 10 -

use of dispersants‖ and expressed EPA’s belief that ―we can reduce the amount of dispersant 

applied by as much as half, and I think probably 75%, maybe more.‖54 Second, she expressed 

dissatisfaction with BP’s efforts to analyze other dispersant options.55 Third, she announced, 

EPA would perform its own tests to verify BP’s data and to ―determine the least toxic, most 

effective dispersant available in the volumes necessary for a crisis of this magnitude.‖56

Two days later, Administrator Jackson sent a letter to David Rainey of BP criticizing 

BP’s inadequate compliance with the May 20, 2010 directive, which had instructed BP ―to

analyze alternative dispersants for toxicity and effectiveness and report back within 24 hours.‖57

―Because we believe your analysis of potential alternative dispersants was insufficient,‖ she 

wrote, ―the EPA is performing its own scientific verification of the data BP presented.‖58 EPA 

said it would make laboratory comparisons with Gulf of Mexico species, including a silverside 

fish and a mysid shrimp.59 EPA would also identify a test for endocrine disrupters.60 

Administrator Jackson’s letter continued: ―Furthermore, as we discussed, the federal 

government, led by the Coast Guard, is reiterating its instructions to BP to take immediate steps 

to significantly scale back the overall use of dispersants.‖61 A May 26, 2010 directive provided 

that ―BP shall eliminate the surface application of dispersants‖ except in ―rare cases where there 

may have to be an exemption.‖62

On June 30, 2010, EPA released results of its own testing of eight dispersants.63 EPA 

had conducted acute toxicity tests with two Gulf of Mexico aquatic species, and in vitro

cytotoxicity (cell damage) and endocrine screening assays using human cell lines. EPA’s results 

indicated that none of the eight dispersants displayed significant endocrine disrupting activity. It

also suggested that Corexit 9500 was not overall more toxic than alternatives: ―While the 

dispersant products alone—not mixed with oil—have roughly the same impact on aquatic life, 

JD-2000 and Corexit 9500 were generally less toxic to small fish and JD-2000 and SAF-RON 

GOLD were least toxic to mysid shrimp.‖64

The effort to scale back use of dispersants had some effect. During the week of May 18, 

2010, BP applied 190,000 gallons total.65 The following week, it applied roughly two-thirds as 

 

54 Id.

55 Id.

56 Id.

57 Letter from Lisa P. Jackson, EPA Administrator, to David Rainey, V.P. of Gulf of Mexico Exploration, BP 

Exploration and Production (May 26, 2010), available at http://www.epa.gov/bpspill/dispersants/Rainey-letter052610.pdf.

58 Id.

59 See id.

60 See id.

61 Id.

62 See EPA, DISPERSANT MONITORING AND ASSESSMENT DIRECTIVE FOR SUBSURFACE DISPERSANT APPLICATION–

ADDENDUM 3 (May 26, 2010), available at http://www.epa.gov/bpspill/dispersants/directive-addendum3.pdf.

63 See Press Release, Deepwater Horizon Incident Joint Information Center, EPA Releases First Round of Toxicity 

Testing Data for Eight Oil Dispersants (July 1, 2010), available at

http://www.restorethegulf.gov/release/2010/07/01/epa-releases-first-round-toxicity-testing-data-eight-oildispersants. The dispersants were Corexit 9500A, Dispersit SPC 1000, JD-2000, Nokomis 3-AA, Nokomis 3-F4, 

SAF-RON GOLD, Sea Brat #4 and ZI-400. 

64 Id. 

65 See Restore the Gulf Estimates. 
Originally Released October 6, 2010

Updated January 11, 2011

- 11 -

much (135,000 gallons).66 Surface use fell from 120,000 gallons the week of May 18, 2010, to 

40,000 gallons the week of May 25, 2010, although it then rose again and remained steady for 

several weeks at 80-90,000 gallons per week. By the end of May, BP had used a total of 950,000 

gallons of dispersants, of which 740,000 were applied on the surface and 210,000 subsea.67 As 

the following table shows, use of dispersants remained at a roughly constant level through most 

of June, but then began to decline again later in the month through early July:

Table 1: Weekly Use of Dispersants June 1-July 1268

Despite the joint Coast Guard-EPA directive that BP ―eliminate the surface application of 

dispersants‖ except in ―rare cases where there may have to be an exemption,‖ the use of surface 

dispersants was not eliminated after May 26, 2010. The ―rare cases‖ were not very rare. Until 

late June, surface use in most weeks remained at about 40% of the pre-directive rate. The 

directive remained in effect despite suggestions that it be modified as responders became aware 

that the oil flow was much larger than previously believed.70

 

66 Id.

67 Id.

68 Id. Note that ―totals‖ may not exactly correspond to the sum of components, apparently due to rounding, use of 

different data sources, or minor calculation errors in the original source. Weekly totals in the table are calculated by 

subtracting the government figures for cumulative use between weeks; the results do not always correspond to the 

amounts reported separately for subsea and surface use. The discrepancies in the government figures appear to be 

relatively minor, however.

69 The ―lower bound‖ refers to the fact that, according to the source, use was ―more than‖ these amounts. 

70 Letter from Rear Admiral James A. Watson, Federal On-Scene Coordinator, to Regional Response Team, Federal 

Region VI (June 22, 2010), available at http://markey.house.gov/images/DISPERSANTDOCUMENTSJUNE22-

24.pdf.

Week Weekly Use of Dispersants 

(gallons)

Total Use of Dispersants to 

Date (gallons) (lower bound)69

June 1 – June 7 171,000 (total):

50,000 (surface)

121,000 (subsea)

1.12 million (total): 

790,000 (surface) 

331,000 (subsea)

June 8 – June 14 163,000 (total):

92,000 (surface)

71,000 (subsea)

1.28 million (total): 

882,000 (surface)

402,000 (subsea)

June 15 – June 21 169,000 (total):

88,000 (surface)

80,000 (subsea)

1.45 million (total): 

970,000 (surface)

482,000 (subsea)

June 22 – June 28 112,000 (total):

30,000 (surface)

83,000 (subsea)

1.56 million (total):

1 million (surface)

565,000 (subsea)

June 29 – July 5 145,000 (total):

40,000 (surface)

92,000 (subsea)

1.71 million (total):

1.06 million (surface) 

645,000 (subsea)

July 6 – July 12 90,000 (total)

10,000 (surface)

90,000 (subsea)

1.8 million (total)

1.07 (surface)

735,000 (subsea)
Originally Released October 6, 2010

Updated January 11, 2011

- 12 -

After the well was capped on July 15, 2010, there was virtually no further use of 

dispersants. By that time, BP had applied a total of 1.84 million gallons, of which 1.07 million 

gallons were applied on the surface and 771,000 gallons were subsea.

71 As Table 1 indicates, the 

amounts injected underwater became larger than the amounts applied to the surface during the 

last three weeks. The week before the well was capped, only about 10% of dispersants used 

were applied to the surface. NOAA estimated in a November 23, 2010 report that approximately 

16% of the oil emanating from the well was chemically dispersed, either subsea or on the 

surface, while 23% evaporated or dissolved, and 13% was dispersed naturally at the wellhead.

72

Although the use of dispersants had ended earlier in the month, debate about the use of 

dispersants surfaced again at the end of July. On July 12, 2010, Admiral Allen’s Chief of Staff 

informed Rep. Edward Markey that dispersants were used ―only when absolutely necessary to 

preserve the health and safety of workers at the well site and to minimize shoreline impacts.‖73

On July 30, 2010, Rep. Markey sent a letter to Admiral Allen pointing to more than 74 BP 

exemption requests in 48 days, of which all but ten were fully approved by the Coast Guard. 

Rep. Markey alleged ―these applications appear to be rubber stamped by the Coast Guard.‖74

The next day, in a conference call, Admiral Allen and Administrator Jackson replied that 

they had cooperated closely and nearly attained the goal of a 75% reduction in dispersant use.75 

On August 1, 2010, Admiral Allen said in a press conference that field commanders on a caseby-case basis decided to use dispersants where surveillance aircraft spotted oil and no other 

method of cleaning it up was available in the area. Admiral Allen noted that the decision to use 

the dispersants did not rest with BP. Rather, he said, ―it’s a decision by the Federal on-scene 

coordinator‖ through a ―very disciplined doctrinal process.‖76

In a CNN interview the following day, Admiral Allen elaborated upon the working 

relationship between Coast Guard and EPA regarding the use of dispersants. According to the 

Admiral, he and Administrator Jackson ―talk daily about dispersant use,‖ the Coast Guard 

―ha[s]n’t ignored EPA’s guidelines,‖ and he was ―satisfied‖ with dispersant use in the Deepwater 

Horizon disaster.77 Relatedly, CNN quoted an EPA spokesman as saying that, ―[w]hile EPA may 

not have concurred with every individual waiver granted by the federal on-scene coordinator, the 

agency believes dispersant use has been an essential tool in mitigating this spill’s impact, 

preventing millions of gallons of oil from doing even more damage to sensitive marshes, 

 

71 Id.

72 See infra note 95 and text accompanying.

73 Letter from Peter Gautier, Chief of Staff, National Incident Command, to Rep. Edward J. Markey (July 12, 2010), 

available at http://markey.house.gov/docs/07-15-10cgtoejmdispersants.pdf.

74 Letter from Rep. Edward J. Markey to Admiral Thad W. Allen, National Incident Commander, United States 

Coast Guard (July 30, 2010), available at http://markey.house.gov/docs/07-30-10ejmtocgdispersants.pdf. 

75 Matthew L. Wald, Despite Directive, BP Used Dispersant Often, Panel Finds, N.Y. TIMES (Aug. 1, 2010). 

Commission staff has learned from EPA staff that this claim was based on a comparison to the highest daily rate of 

use, rather than a comparison of amounts used on a weekly basis. See Table 1.

76 Press Conference with Thad Allen, National Incident Commander, U.S. Coast Guard (Aug. 1, 2010), available at 

http://www.restorethegulf.gov/release/2010/08/01/transcript-press-briefing-national-incident-commander-admiralthad-allen-0.

77 Allen ‘satisfied’ with dispersant use in Gulf oil disaster, CNN (Aug. 2, 2010),

http://edition.cnn.com/2010/US/08/01/gulf.oil.spill/index.html#fbid=CAHE69XH089. 
Originally Released October 6, 2010

Updated January 11, 2011

- 13 -

wetlands and beaches and the economy of the Gulf coast.‖78 These statements suggested that 

coordination with EPA did not mean that the Federal On-Scene Coordinator heeded EPA’s 

advice on all occasions. Given the pre-approval of dispersant use, the Federal On-Scene 

Coordinator was not required to do so.

II. Assessing the Federal Government’s Use of Dispersants During the Deepwater 

Horizon Spill

It is too early to assess many aspects of the federal government’s use of dispersants in 

response to the Deepwater Horizon spill between the explosion on April 20, 2010, and the 

containment of the well on July 15, 2010. In making any assessment, moreover, it is important 

to distinguish between three inquiries: (1) whether the federal government adequately prepared 

in advance for the possible use of dispersants to address such a spill; (2) whether, once the spill 

occurred, the government’s decisions regarding the use of dispersants were reasonable in light of 

the resources and the information then available; and (3) whether, with the benefit of hindsight, 

those government decisions, regardless of their reasonableness or unreasonableness when made, 

resulted in benefits that outweighed harms.

A. The Adequacy of the Government’s Contingency Planning

The first of these three questions is the one most easily answered. The government was 

not adequately prepared for the use of dispersants to address such a large oil spill. 

Notwithstanding the National Contingency Plan’s express requirements for planning regarding 

the use of dispersants, including pre-authorization to deal with emergencies, EPA clearly did not 

anticipate the potential demands of an oil spill of the kind the nation faced after the Macondo 

well explosion. In particular, EPA did not consider, in its roles on the National Response Team 

and the relevant Regional Response Teams, the possibility that dispersants might have to be used 

in the massive volumes required in the Gulf. And EPA did not consider the distinct possibility 

that massive volumes of dispersants might be needed at the subsea level. 

Neither omission can be justified on the ground that a major subsea spill was wholly 

unforeseeable. The oil and gas industry has been extracting high volumes of oil from reservoirs 

in the Gulf for twenty years. This is not a new, unanticipated development. Nor is deepwater 

drilling. Yet, just as the Minerals Management Service and industry failed to plan adequately for 

a blowout of this magnitude and duration (topics discussed in other work by the Commission and 

its staff), EPA did not consider adequately the challenges of dispersant use flowing from largescale drilling operations, especially operations in deepwater. EPA did not require studies or 

testing that took account of the likely amounts or locations of dispersant use necessary in the 

event of a well blowout, in particular a deepwater blowout. 

Nor had NOAA adequately planned for such an event. NOAA has significant 

responsibility to provide scientific support for national response and contingency planning

pursuant to the Clean Water and Oil Pollution Acts.

79

 Its related expertise arises out of its work 

 

78 Id.

79 40 C.F.R. §§ 300.145, 300.175, 300.210.
Originally Released October 6, 2010

Updated January 11, 2011

- 14 -

in many areas, including its duties under the Endangered Species Act,80 Marine Mammal 

Protection Act,81 and Magnuson-Stevens Fishery Conservation and Management Act82 to protect 

endangered and threatened species of marine life, marine mammals, and the nation’s fisheries in 

U.S. waters. Yet NOAA had also not previously evaluated the potential impacts of voluminous 

and extended use of dispersants on marine life and the nation’s fisheries.

As a result, the National Incident Commander, the EPA Administrator, and the NOAA 

Administrator were seriously handicapped when the Macondo well explosion occurred and 

decisions had to be made immediately in the absence of adequate contingency planning. These 

officials had to make difficult choices with insufficient information about the critical trade-offs 

identified by the National Academy of Sciences for the use of dispersants: the value of the 

dispersants in reducing the harm caused by released oil versus the potential risks of harm from

the dispersants themselves. The limited toxicity data they possessed was questionable and

limited to acute lethal effects on two estuarine species.

83

 It did not consider potential

environmental persistence resulting from repeated or continuous sublethal effects, such as 

endocrine disruption.

The absence of adequate contingency planning had a further negative impact on the 

effectiveness of the government’s response. It made unclear the lines of authority between 

various federal agencies in determining whether dispersants should be used. In particular, there 

was uncertainty regarding the extent to which the Coast Guard needed to secure EPA’s approval 

before permitting the use of dispersants. Notwithstanding the lack of any requirement that the 

Federal On-Scene Coordinator defer to EPA on the use of dispersants at the surface (given 

EPA’s pre-approval), and the lack of a clear requirement with regard to the subsea, EPA decided 

to exercise substantial control over both types of dispersant use, which at times led to delays in 

necessary decision-making (and, according to Coast Guard responders, to some avoidable 

shoreline impacts from oil as a result of the inability to use dispersants quickly).84

B. The Reasonableness of the Government’s Decision To Authorize the Use of 

Dispersants at the Time It Was Made

As described above, the reasonableness of the federal government’s decision to authorize 

the use of dispersants is distinct from the questions of whether there was adequate contingency 

 

80 7 U.S.C. §§ 1531 et seq.

81 16 U.S.C. §§ 1361 et seq.

82 16 U.S.C. §§ 1801 et seq.

83 See supra note 25; Biello, Fighting Pollution with Pollution (quoting toxicologist Carys Mitchelmore’s statement 

that ―[i]f you think the data on COREXIT is bad, try to find any decent toxicology data on the alternatives‖). 

84 In interviews with Commission staff, responders stated that EPA representatives on the scene, unlike 

representatives from other government agencies, were not empowered to make binding decisions notwithstanding 

EPA’s claims of authority over the use of dispersants. Instead, those EPA representatives had to relay information 

to agency superiors, which inevitably delayed decisions that needed to be made quickly. In addition, these response 

participants from other federal agencies stated that the EPA on-scene representatives sometimes lacked the 

necessary experience in oil spill response and that EPA scientists with such experience were not being adequately 

consulted in EPA’s decision-making process. Finally, these individuals expressed an overall concern that EPA’s 

internal decision-making procedures were simply not organized to make the kind of rapid decisions necessary in the 

oil spill context, which are quite different from the lengthier deliberative processes that mark the kind of long-term 

regulatory rulemakings in which EPA more routinely engages. 
Originally Released October 6, 2010

Updated January 11, 2011

- 15 -

planning (which there was not) and whether the decision ultimately turned out to be prudent.

This inquiry instead focuses on whether the government acted reasonably given the limited 

knowledge and resources that it possessed at the time. Based on the information currently 

available to the Commission staff, we cannot conclude that the government acted unreasonably 

in deciding to approve the use of massive volumes of dispersants at the subsea and surface. 

Because federal agencies had failed to plan adequately, they did not possess the scientific 

information that officials most certainly would have wanted to guide their choices. They had to 

make choices nevertheless: Millions of gallons of oil were flowing from the Macondo well into 

the Gulf of Mexico every day, imperiling the responders who worked in the immediate vicinity 

of the spill, residents living along the Gulf Coast, the Gulf marine ecosystem, and the fishing and 

tourism industries.

Given the conditions under which officials like Admiral Allen and EPA Administrator 

Jackson were acting, there is no clear evidence that their decisions to authorize high volumes of 

dispersants, including at the subsea, were unreasonable. They instead appear to have acted 

reasonably in the difficult circumstances in which they were placed. For instance, officials 

directed the Regional Response Teams to seek input as quickly as possible from fifty expert 

scientists.85 On June 4, 2010, the experts reported a consensus that ―use of dispersants and the 

effects of dispersing oil into the water column has generally been less environmentally harmful 

than allowing the oil to migrate on the surface into the sensitive wetlands and near shore coastal 

habitats.‖86 In the experts’ view, though gaps in relevant information existed, the environmental 

trade-off between the deep-ocean ecosystem and the shoreline made dispersants an acceptable 

choice.

There are, however, three caveats regarding the decision-making process. First, 

Commission staff heard repeated reports that EPA could have done a better job of ensuring that 

its on-scene representatives had both the expertise and the authority to make decisions regarding 

the use of dispersants, so as to avoid the delays that reportedly occurred because of the absence 

of such authority and expertise. For example, the Commission staff has heard from two sources 

that EPA waited until late June to permanently install one of the Agency’s most senior officials 

at the Unified Command headquarters located in Robert and then New Orleans, Louisiana.87

The second caveat relates to implementation of the planned approach for decisionmaking regarding dispersants. The planning documents for the area require the Regional 

Response Teams to make decisions about novel uses of dispersants, upon request from the 

Federal On-Scene Coordinator. Here, as the issue of dispersant application became more and 

 

85 In May, the Regional Response Teams asked for scientific input to direct their future dispersant use and, to that 

end, fifty experts met together on May 26 and 27, 2010, at Louisiana State University for the ―Deepwater Horizon 

Dispersant Use Meeting.‖ Coastal Response Research Center, DEEPWATER HORIZON DISPERSANT USE MEETING 

REPORT 5 (June 4, 2010) available at http://www.crrc.unh.edu/dwg/dwh_dispersants_use_meeting_report.pdf. In 

the meeting, the experts split into four breakout groups: (1) efficacy and effectiveness of surface and deep ocean 

dispersants use; (2) physical transport and chemical behavior of dispersants and dispersed oil; (3) exposure pathways 

and biological effects resulting from deep ocean application of dispersants; and (4) exposure pathways and 

biological effects resulting from surface application of dispersants. Id.

86 Id. at 4.

87 Interviews with government officials.
Originally Released October 6, 2010

Updated January 11, 2011

- 16 -

more prominent in the media and for the public, the decisions to apply both surface and subsea 

dispersants were taken out of hands of the Regional Response Teams. Admiral Allen and 

Administrator Jackson to a large extent bypassed the National and Regional Response Team 

structures and instead issued decisions regarding dispersant policy through joint directives. 

Though this reflected the high level at which the issues were being evaluated, it was outside of 

the process that responders were supposed to implement.

These two caveats aside, the Commission staff has reason to believe that there was 

generally a sound and cooperative working relationship between the federal agencies on the

question of dispersants.

88 While the National and Regional Response Teams did not play the 

coordinating and decision-making role envisioned under the National Contingency Plan, the 

Federal On-Scene Coordinators worked directly with EPA and NOAA on dispersant policy. 

That coordination resulted in, among other things, the specific designation of subsea dispersants 

as an appropriate response technology subject to stringent limits on amounts as well as expansive 

testing and monitoring guidelines. In addition, the Federal On-Scene Coordinators and EPA 

worked together to reduce significantly the application of surface dispersants and to resolve the 

disagreements between the two agencies.

The third caveat relates to the role of BP. The fact that BP itself (or its oil spill response 

contractors) directly applied the dispersants authorized by the federal government led to the 

impression that BP rather than federal officials was in charge of decisions regarding dispersant 

use. Commission staff has not discovered any evidence that such a usurpation of government 

authority occurred. Nor could Commission staff conclude, based on interviews with Coast 

Guard responders, that BP or its contractors ever intentionally violated government directives 

regarding dispersant use (e.g., regarding the permitted locations for such use). Yet, the 

impression remained and fueled public distrust of the decision to use dispersants. 

C. The Prudence, in Hindsight, of the Federal Government’s Decision To 

Permit Use of High Volumes of Dispersants at the Surface and Subsea

It is too soon to answer this final question with the degree of certainty necessary for 

scientific analysis. The gap between what federal government officials should know prior to the 

use of high volumes of dispersants at the surface and subsea and what they in fact know has 

begun to narrow. But closing that gap will require rigorous scientific inquiry based on years of 

data collection and analysis, followed by the essential process of peer review, before any 

conclusions can be drawn upon which future government officials can safely rely. 

With this crucial limitation in mind, EPA’s preliminary analyses do not suggest that the 

government’s use of dispersants caused major problems. Just the opposite, they support the 

possibility that the benefits of dispersant use outweighed the costs. 

First, it appears that the subsea use of dispersants served an important function by 

increasing the safety of the working conditions faced by responders in the immediate vicinity of 

 

88 The Unified Command’s working relationship with the state of Louisiana on the issue of dispersant use may not 

have been as cooperative. Commission staff heard in multiple interviews with state and federal government officials 

that Louisiana disagreed with the Unified Command’s decision to apply dispersants subsea. 
Originally Released October 6, 2010

Updated January 11, 2011

- 17 -

the spill. That group included individuals working on containment efforts—to cap the well—and 

those seeking to recover, burn, and skim oil. The very real concern had been that high 

concentrations of volatile organic compounds within the oil would be a serious safety and health 

hazard to response workers. The use of subsea dispersants, by reducing the volume and 

concentration of the oil reaching the surface, likewise reduced those associated risks.89

Second, EPA’s subsequent toxicity tests, while still preliminary, have not revealed major 

problems. On August 2, 2010, EPA released the results of additional tests on the toxicity of 

dispersants, which the Agency contended ―confirm that the dispersant used in response to the oil 

spill in the gulf, Corexit 9500A, is no more or less toxic than the other available alternatives.‖90 

The EPA report itself concluded: 

Overall, the dispersants/L[ouisiana] S[weet] C[rude]mixtures were classified as being 

highly toxic to moderately toxic depending on the test species and dispersant. The ZI400/ L[ouisiana] S[weet] C[rude] mixture was the exception and would be considered 

only slightly toxic to Menidia. Corexit 9500A, the dispersant that has been applied 

offshore at the surface and in the deep ocean, falls into the moderately toxic category for 

both species. For all eight dispersants in both test species, the dispersants alone were less 

toxic than the dispersant-oil mixture.91

Finally, EPA also reported on August 2, 2010, that the dispersants seemed to have 

succeeded in protecting the coastal area from greater contamination from the oil spill. The 

Agency referred to ―fluorescence data that indicated the dispersants are working to keep the oil 

away from the shore. . . . [T]he dispersants are working to keep oil off our precious shorelines 

and away from sensitive ecosystems.‖92 The Agency further noted that ―EPA monitoring has not 

found dispersant chemicals in water or sediment near coasts or wetlands.‖93

On August 4, 2010, experts from NOAA, the National Institute of Standards and 

Technology, and the United States Geological Survey released two reports that lent support to 

the claim that dispersants decreased the harms that might have otherwise resulted from the oil 

spill, by indicating that a significant percentage (8%) of the oil was chemically dispersed: BP 

Deepwater Horizon Oil Budget: What Happened to the Oil? and a supporting document entitled

Deepwater Horizon MC252 Gulf Incident Oil Budget (collectively, the Oil Budget).94 On 

 

89 Interviews with government officials. EPA staff has told Commission staff that, while decreasing volatile organic 

compounds at the surface was not a primary justification for permitting subsea dispersant use, it was an important 

benefit that became apparent after use commenced, even without conclusive proof of a causal link between subsea 

use and the reduction.

90 See DISPERSANTS TOXICITY Q&A.

91 EPA, COMPARATIVE TOXICITY OF LOUISIANA SWEET CRUDE OIL (LSC) AND CHEMICALLY DISPERSED LSC TO 

TWO GULF OF MEXICO AQUATIC TEST SPECIES (July 31, 2010), available at 

http://www.epa.gov/BPSpill/reports/phase2dispersant-toxtest.pdf. 

92 Conference Call with Paul T. Anastas, EPA Assistant Administrator (Aug. 2, 2010), available at 

www.epa.gov/bpspill/dispersants/conference-call-transcript-08022010.pdf [hereinafter Anastas Conference Call]. 

Later data supports this conclusion about oxygen levels. See Paul Voosen & Katie Howell, Gulf Spill Roundup:

Subsurface Oil Increasingly Difficult to Detect—NOAA, E& E NEWS (Sept. 2, 2010).

93 See Anastas Conference Call. 

94 Dr. Jane Lubchenco et al., BP DEEPWATER HORIZON OIL BUDGET: WHAT HAPPENED TO THE OIL? (Aug. 4, 2010), 

available at http://www.noaanews.noaa.gov/stories2010/PDFs/OilBudget_description_%2083final.pdf; DEEPWATER 
Originally Released October 6, 2010

Updated January 11, 2011

- 18 -

November 23, NOAA released a new version of the Oil Budget: Oil Budget Calculator 

Technical Documentation, a peer-reviewed report of over 200 pages that gave the formulas used 

and updated the percentages in the original budget.95 The new version’s biggest change was its 

estimate of the amount of oil chemically dispersed, which doubled from 8 to 16%. Outside 

scientists continue to debate the fate of the oil and the merits of the government’s Oil Budget. 

One major focal point of criticism has been the failure of the Oil Budget to analyze and take 

account of biodegradation, which chemical dispersants are intended in part to promote. Several 

peer-reviewed reports have offered differing perspectives on how quickly subsurface Macondo 

oil is biodegrading.96 

The ongoing debate regarding the fate of subsurface Macondo oil underscores the futility 

of trying now to evaluate conclusively the government’s decision to use high volumes of 

dispersants. Even without application of dispersants subsea, the turbulent mixing of oil and gas 

from the wellhead could have created the deepwater plume of dispersed oil. According to the 

Oil Budget, subsea dispersant use only added to the amount of oil in the plume.97 As more 

scientific research occurs, a better understanding of the degradation and impacts of this naturally 

and chemically dispersed oil will undoubtedly emerge.

98

 It will also take time and research to 

 

HORIZON MC252 GULF INCIDENT OIL BUDGET (Aug. 4, 2010), available at

http://www.noaanews.noaa.gov/stories2010/PDFs/DeepwaterHorizonOilBudget20100801.pdf.

95 NOAA, OIL BUDGET CALCULATORTECHNICAL DOCUMENTATION (Nov. 2010), available at

http://www.restorethegulf.gov/sites/default/files/documents/pdf/OilBudgetCalc_Full_HQ-Print_111110.pdf.

96 These include: A report from a team at Woods Hole Oceanographic Institution, which discovered a deep sea ―oil 

plume‖ and suggested that rapid biodegradation might not be occurring (Richard Camilli et al., Tracking 

Hydrocarbon Plume Transport and Biodegradation at Deepwater Horizon, SCIENCE EXPRESS (Aug. 19, 2010)); an 

article published by a team from the Lawrence Berkeley National Laboratory, which found evidence of increased 

microbial respiration within the plume and concluded that biodegradation rates were ―faster than expected‖ (Terry 

C. Hazen et al., Deep-Sea Oil Plume Enriches Indigenous Oil-Degrading Bacteria, SCIENCE EXPRESS (Aug. 24, 

2010)); a report by Valentine et al., which suggested that, while most of the initial degradation was of natural gas 

rather than liquid oil, this could prime bacteria to degrade other hydrocarbons in the aging plume (David L. 

Valentine et al., Propane Respiration Jump-Starts Microbial Response to a Deep Oil Spill, SCIENCE EXPRESS (Sept. 

16, 2010)); and a government report concluding that oxygen levels were not decreasing because the oxygen depleted 

by biodegradation was being replenished through the mixing of plume water with surrounding waters (JOINT 

ANALYSIS GROUP, REVIEW OF PRELIMINARY DATA TO EXAMINE OXYGEN LEVELS IN THE VICINITY OF MC252#1

(Aug. 16, 2010), available at

http://ecowatch.ncddc.noaa.gov/JAG/files/JAG_Oxygen_Report%20FINAL%20090410.pdf).

97 See OIL BUDGET CALCULATOR TECHNICAL DOCUMENTATION at 21, 30.

98 On August 13, 2010, Admiral Allen issued a directive calling for an extensive study to better understand how 

much oil remains in the Gulf and its impacts on the marine ecosystem. Press Briefing, Admiral Thad Allen (Aug. 

13, 2010), http://www.restorethegulf.gov/release/2010/08/13/transcript-press-briefing-national-incident-commanderadmiral-thad-allen. After several months of subsea sampling and analysis, the government issued its report on 

December 17. Operational Science Advisory Team, Unified Area Command, SUMMARY REPORT FOR SUB-SEA AND 

SUB-SURFACE OIL AND DISPERSANT DETECTION: SAMPLING AND MONITORING (Dec. 17, 2010). The report 

concludes that: (1) after August 3, the amount of hydrocarbons in the Gulf from the Macondo well (as opposed to 

other sources, like natural seeps) has not exceeded EPA benchmarks for human health and aquatic life; (2) the 

application of dispersants to combat the spill did not cause levels of the chemical compounds found in dispersants to 

exceed EPA benchmarks in the nearshore and offshore environments; (3) hydrocarbon levels in deep-water 

sediments within 3 kilometers of the wellhead did exceed the established benchmark for aquatic life; and (4) there 

were ―tar mats‖—essentially oil mixed with sediment—in nearshore ―shallow sub-tidal areas,‖ id. at 48. In addition, 

the report considered peer-reviewed studies discussing biodegradation (including those cited in note 96, supra) and 

concluded that ―[t]he degradation rates for the complete mixture of compounds that characterize [Macondo] oil have 

not yet been determined.‖ Id. at 47.
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Updated January 11, 2011

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determine whether the dispersants themselves, used in such high volumes and subsea, have any 

longer-term detrimental effects on marine life or public health. For now, there has not been 

compelling evidence of harmful effects to indicate that decision-makers misjudged the risks 

versus the benefits of applying dispersants. 

III. Issues for Commission Consideration

This final part describes policy implications for Commissioner consideration that arise

from possible lessons learned from the use of dispersants during the Deepwater Horizon spill 

response. These lessons and related policy implications are not intended as exhaustive of those 

that may flow naturally from the above analysis, but merely illustrative of the possibilities.

A. Further Research

Perhaps more than anything, the Deepwater Horizon experience with dispersants reveals 

the paucity of the kind of information that government officials need to make intelligent 

decisions about dispersant use in response to an oil spill. Although the absence of such

information was well known before April 20, 2010, its practical effect had not been so glaringly 

realized.

As of 1999, EPA reported, ―few long-term environmental effects tests have been 

conducted after a dispersant application.‖99 In 2005, the National Research Council noted that 

U.S. research funding to support oil spill response was ―extremely limited and declining‖ (with 

an annual total below $10 million).100 The Council called on the relevant federal agencies to 

develop an integrated research plan focusing on peer-reviewed information.101 Only a quarter of 

the $40 million in proposed research funding on dispersants and chemically dispersed oil ever 

materialized.102

The Deepwater Horizon oil spill confirms the urgency of these prior funding requests and 

suggests additional needs as well, including, for example, studies about the impacts of high 

volumes of dispersants, subsea impacts, and the long-term fate and effects of dispersants and 

dispersed oil—none of which appear to have been meaningfully addressed or at least addressed 

to the extent that now seems essential.103 Efforts are ongoing to learn more about dispersant 

impacts in the Gulf. On August 3, 2010, the National Incident Commander recommended a 

detailed monitoring strategy, with NOAA as the operational lead, to evaluate the ―distribution of 

indicators of break-down products of dispersants used in oil spill response activities.‖104

 

99 EPA, UNDERSTANDING OIL SPILLS AND OIL SPILL RESPONSE 13 (1999). 

100 NRC Report at 4.

101 Id.

102 Id. at 5-8; see Elana Schor, Oil Spill Dispersants Shifting Ecosystem Impacts in Gulf, Scientists Warn, N.Y.

TIMES (July 30, 2010) (―[Dr. Nancy] Kinner said the National Research Council’s report outlined a $40 million plan 

for dispersant research, but a quarter of the money materialized over the past five years.‖).

103 See CRRC Report at 7 (confirming need for research into ―chemical dispersion,‖ including understanding ―the 

long-term fate of chemically dispersed oil‖ and ―investigating...multiple oil (including heavy) and dispersant 

types.‖). 

104 Memorandum from Admiral Thad. Allen, National Incident Commander, Deepwater Horizon Response, to Rear 

Admiral Paul Zukunft, Federal On-Scene Coordinator (Aug. 3, 2010), available at 
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Updated January 11, 2011

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The development of dispersant alternatives should also be a priority. So-called ―green 

chemistry‖ carries promise. Dispersants would seem to be a potentially important market for 

efforts to find new chemical products that are effective, less toxic, and more readily 

biodegradable.

Research and development, of course, requires funding. Offshore drilling provides a 

context within which substantial funding should be in reach. The nation’s need for oil and gas 

from the outer continental shelf is undeniable. But so too are the massive revenues those 

reserves yield in the market and the harm, as recent events demonstrate, if drilling goes awry. 

The smallest fraction of those revenues, whether charged directly to industry or originating in 

what the government already receives, would provide a major benefit in terms of potential to 

mitigate the impact of oil spills from offshore drilling.

B. Government Contingency Planning and Decision-Making Procedures

Government contingency planning for the use of dispersants was, as described, lacking. 

The federal agencies charged with planning did not adequately anticipate the need for dispersants 

in high volumes and at subsea locations. Federal officials must now survey existing and future 

offshore facilities and locations and consider systematically the particular challenges they 

present for spill response. In the future, officials should not find themselves similarly faced in 

the future with the need to make immediate decisions in the absence of adequate information.

Contingency planning reform should extend to rethinking both testing requirements and 

the use of pre-approved lists of dispersants. Plainly, the pre-approval process has significant 

advantages in the immediate aftermath of an oil spill and for that reason should not be 

abandoned. Indeed, it should be more rigorously applied by ensuring that those dispersants that 

are pre-approved are subject to more comprehensive testing.

There is clearly a need for expanded testing and greater information regarding dispersants 

placed on the National Contingency Plan Product Schedule, to include characteristics such as 

effectiveness and persistence under different environmental conditions. Testing should also be 

based on the use of higher volumes, including subsea. Moreover, current EPA protocols for 

industry testing may not be adequate to yield reliable and consistent results.105 Given the everchanging nature of the underlying science, periodic updating of testing and testing protocols is 

essential. 

The Deepwater Horizon spill also suggests the possibility of including temporal, spatial, 

and/or volumetric limits on the pre-approval of dispersants for use in a geographic area. It is one 

thing to pre-approve based on the frequently reliable assumption that the response action will be 

 

http://app.restorethegulf.gov/sites/default/files/documents/pdf/NIC-Sub-surface-memo.pdf; see also Press 

Conference with Admiral Thad Allen, National Incident Commander, Deepwater Horizon Response, and Dr. Jane 

Lubchenco, NOAA Administrator (July 27, 2010), available at 

http://www.restorethegulf.gov/release/2010/07/27/transcript-press-briefing-national-incident-commander-admiralthad-allen-and-noaa.

105 See, e.g., Biello, Fighting Pollution with Pollution.
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Updated January 11, 2011

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limited in time, space, and dispersant volume. But, as the Deepwater Horizon spill dramatically 

illustrated, where those assumptions no longer hold, the force of a pre-approval is diminished. In 

particular, there is more reason to allow for federal officials other than the On-Scene 

Coordinator, such as EPA officials who possess particular expertise, to play a role in decisionmaking during the actual response. To that end, contingency planning for the use of dispersants 

during oil spill response should consider distinguishing between types of oil spills, based on their 

temporal duration, spatial reach, and volume.

With greater authority comes greater responsibility. During the Deepwater Horizon spill, 

there were reports that on-scene EPA representatives lacked the expertise and authority essential 

in a response action. Any enhancement of EPA’s authority therefore must be coupled with 

assurances that EPA has the resources and clear lines of decision-making authority necessary for 

effective spill response. Ultimately, any recommendations for changes in the unified command 

structure should turn not just on the recent experience with the use of dispersants, but on a more 

cross-cutting inquiry, which is the subject of separate work by the Commission and its staff. The 

issues surrounding dispersant use should inform that broader set of recommendations.

Finally, federal officials must from the outset leave no question in the public’s mind 

regarding who is in charge during an emergency response, especially when, as happened with 

dispersants, public concern with the wisdom of the government’s decisions is great. Here, a 

mistaken impression was created in the minds of too many that BP was making the decisions 

based on its own interests. That misimpression fueled the controversy over the potentially 

harmful impacts of dispersants, which itself harmed the public, creating real fears that had 

economic consequences to the extent they affected tourism and other consumer choices. In the 

future, government officials must leave no doubt that they, and not private industry, are making 

difficult decisions.