Who Was at Fault for the Deepwater Horizon Disaster?

A federal court assigned 67% of the fault for the Deepwater Horizon disaster to BP, 30% to rig owner Transocean, and 3% to cement contractor Halliburton.¹ The April 20, 2010 blowout at the Macondo well killed 11 workers and released roughly four million barrels of crude over 87 days. It was not caused by any one mistake. A chain of cost-driven decisions, equipment failures, and missed warning signs ran through all three companies, and the court’s percentages reflect how much of that chain each one owned.

The Four Failures Behind the Blowout

Investigators traced the disaster to four sequential failures. The cement at the bottom of the well failed to seal the hydrocarbon zone. The negative pressure test failed to catch the bad seal. The crew failed to detect that the well was flowing until gas was almost at the rig floor. And the blowout preventer failed to shut the well in.² Each failure sat with a different company, and together they turned a challenging deepwater well into a catastrophe.

BP: 67% at Fault

BP was the operator and leaseholder of the Macondo well. It controlled the drilling plan, set the schedule, and made the key engineering calls.³ That authority produced the largest share of blame. The National Commission on the Deepwater Horizon Oil Spill found that many of BP’s decisions increased risk while saving the company time and money, and that BP never conducted a disciplined analysis of how those stacked-up risks affected the well.

Cost-Driven Engineering Choices

The most-cited example involved centralizers, which keep the well casing centered so cement can flow evenly around it. BP’s own engineers recommended 21. The company ran only six. BP also chose a single long-string production casing running from the seafloor to the bottom of the well, rather than a liner-and-tieback design. The federal court found the casing choice did not directly cause the blowout but noted that initial cost savings “did enter the analysis” when BP made the decision.⁴

Skipped Tests and Misread Warnings

BP decided not to run a cement bond log, a diagnostic that would have shown whether the cement at the bottom of the well had sealed. The test would have cost roughly $128,000 and taken several hours. BP sent the logging crew home without running it.

Then came the negative pressure test, which was supposed to confirm the well was secure before the crew moved on. The readings were anomalous and should have stopped the job. BP’s two highest-ranking supervisors on the rig, the well site leaders, interpreted them as acceptable and let operations continue. The federal court found that both supervisors negligently caused the deaths of the 11 workers.⁵

Transocean: 30% at Fault

Transocean owned the Deepwater Horizon, employed most of the crew, and was responsible for maintaining the rig’s safety equipment, including the blowout preventer. The court’s 30% allocation reflected failures in both areas.

A Blowout Preventer That Could Not Seal

A blowout preventer is the last line of defense. When everything else fails, it is supposed to shear through the drill pipe and seal the well. The Cameron-manufactured unit at Macondo did shear the pipe but could not develop a seal. The upper annular preventer, activated by the crew at about 9:43 p.m., also failed to stop the flow, likely because of erosion in its rubber sealing element. The automated emergency system apparently fired but could not fully close and seal the well either.² Maintaining and testing that device fell to Transocean.

Training and Drill Gaps

A Coast Guard investigation found Transocean’s crew lacked adequate training on when and how to disconnect the rig from the well to avoid an explosion. Gas detectors were not configured to trigger an automatic emergency shutdown of the engines, and the bridge crew had not been trained on when to activate those systems manually. Fire drills were held at the same time on the same day each week, and crew members were sometimes allowed to skip them. Transocean, the Coast Guard concluded, “failed to ensure that its onboard management team and crew had sufficient training and knowledge to take full responsibility for the safety of the vessel.”

Halliburton: 3% at Fault

Halliburton designed and pumped the cement slurry intended to seal the bottom of the well. That cement was the first barrier to fail, which made Halliburton’s work the technical starting point of the disaster. The court still assigned the company only 3%, reflecting its view that Halliburton did not control the broader design and testing decisions that allowed the cement failure to become a blowout.

Unstable Cement

The job used a nitrogen-foamed slurry, chosen because the margin between the pressure needed to control the well and the pressure that would fracture the surrounding rock was narrow. Halliburton did pre-job testing on the foam cement design, but the results were disputed. The National Commission pointed to tests showing the slurry was unstable. Halliburton countered that some of those tests used different formulations than what was actually pumped. Either way, the cement that went into the well did not hold, and hydrocarbons traveled up the wellbore to the rig.

Destroying Simulation Results

After the blowout, Halliburton’s cementing technology director ordered employees to run computer simulations comparing six centralizers against 21. When the results showed little difference between the two options, he ordered them destroyed. A second employee ran similar simulations and was told to “get rid of” those results as well. Halliburton pleaded guilty in 2013 to one count of destruction of evidence, paid the statutory maximum fine, and made a separate $55 million voluntary contribution to the National Fish and Wildlife Foundation.⁶

Other Companies With Exposure

Two other companies carried significant financial exposure but were not part of the court’s fault allocation. Cameron International manufactured the blowout preventer and settled with BP in December 2011 for $250 million, with no admission of liability by either side. Anadarko Petroleum owned a 25% interest in the Macondo lease but did not control operations. Anadarko settled with BP for $4 billion and transferred its entire lease interest to BP.¹

How the Court Reached the Allocation

The multidistrict litigation went to Judge Carl Barbier of the U.S. District Court for the Eastern District of Louisiana.⁷ In September 2014, Barbier found BP grossly negligent and guilty of willful misconduct. That finding carried real weight: under the Clean Water Act, gross negligence raises the civil penalty ceiling to $3,000 per barrel discharged, compared to about $1,100 per barrel for ordinary negligence.⁸ The January 15, 2015 Phase Two ruling then set the final split at 67/30/3.⁹ Transocean was found negligent but not grossly so.

What Being at Fault Cost Each Company

BP pleaded guilty in November 2012 to 14 criminal counts, including 11 counts of felony manslaughter for the workers killed, one count of obstruction of Congress, and two environmental crimes. It agreed to pay $4 billion in criminal fines and penalties, the largest criminal resolution in U.S. history at the time.⁵ On April 4, 2016, a federal judge approved a $20.8 billion global civil settlement with BP covering Clean Water Act penalties, natural resource damages, state economic claims, and federal response costs.¹⁰ By 2018, BP reported total disaster-related costs of roughly $65 billion.

Transocean pleaded guilty in February 2013 to a Clean Water Act violation and paid $400 million in criminal penalties.¹¹ It also paid a $1 billion civil penalty to resolve Clean Water Act claims¹² and reached a separate $212 million settlement with private plaintiffs.

Halliburton’s criminal exposure was limited to the single misdemeanor destruction-of-evidence count, which carried a $200,000 statutory maximum fine alongside its $55 million voluntary contribution.⁶

No Individuals Convicted for the Deaths

The government also charged individual BP employees. None were ultimately convicted. Donald Vidrine and Robert Kaluza, the well site leaders on the rig that night, were charged with involuntary manslaughter for the 11 deaths; those charges were dropped after prosecutors concluded they could no longer meet the legal standard for conviction. David Rainey, BP’s former vice president of exploration in the Gulf and the highest-ranking individual charged, was acquitted in 2015 of lying to federal investigators about the spill rate. Kurt Mix, a BP engineer, was convicted of deleting text messages related to the spill, but his conviction was overturned after a juror introduced outside evidence during deliberations. No individual went to prison for the deaths of the 11 workers.

1
US EPA. Deepwater Horizon – BP Gulf of America Oil Spill
2
US Chemical Safety Board (CSB). Deepwater Horizon Blowout Preventer Failure Analysis Report
3
U.S. Department of the Interior. BP Liable for Reporting and Royalties on Oil and Gas from Leaking Well
4
United States District Court for the Eastern District of Louisiana. Revised Findings of Fact and Conclusions of Law
5
U.S. Department of Justice. BP Exploration and Production Inc. Agrees to Plead Guilty to Felony Manslaughter, Environmental Crimes and Obstruction of Congress Surrounding Deepwater Horizon Incident
6
U.S. Department of Justice. Halliburton Agrees to Plead Guilty to Destruction of Evidence in Connection with Deepwater Horizon Tragedy
7
United States District Court Eastern District of Louisiana. Introduction Description of MDL No. 2179 IN RE: OIL SPILL by the OIL RIG “DEEPWATER HORIZON”
8
Office of the Law Revision Counsel. 33 U.S. Code 1321 – Oil and Hazardous Substance Liability
9
US EPA. Findings of Fact and Conclusions of Law Phase Two Trial
10
National Oceanic and Atmospheric Administration. Deepwater Horizon Oil Spill Settlements: Where the Money Went
11
U.S. Department of Justice. Transocean Pleads Guilty, Is Sentenced to Pay $400 Million in Criminal Penalties
12
US EPA. Transocean Settlement