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Tuesday, December 21, 2010

Deepwater Horizon Oil Spill: The Fate of the Oil

Jonathan L. Ramseur
Specialist in Environmental Policy

The April 20, 2010, explosion of the Deepwater Horizon offshore drilling rig led to the largest oil spill in U.S. waters. Federal government officials estimated that the deepwater well ultimately released (over 84 days) over 200 million gallons (or 4.9 million barrels) of crude oil. Although decreasing amounts of oil were observed on the ocean surface following the well’s containment on July 15, 2010, oil spill response officials and researchers have found oil in other places. A pressing question that has been raised by many stakeholders is where did the oil go?

On August 4, 2010, the federal government released an estimate of the oil spill budget for the Deepwater Horizon incident. On November 23, 2010, the federal government released a peerreviewed “Technical Document” that further explained how the estimates were derived, and in some cases, modified the initial estimates. The oil budget estimates divide the released oil into seven categories, accounting for the following percentages of the total oil released. These categories generally fall into three groups: 

  • Human intervention: direct recovery from the well (17%); in situ burning (5%); skimmed (3%); chemically dispersed (16%). 
  • Natural Processes: naturally dispersed (13%); evaporated or dissolved (24%). 
  • Other (22%): refers to the oil remaining after subtracting the above estimates from the total estimated release; possible fates include remaining in the water column, settling to the sea floor, mixing with sediment, ingested by microbes, or collected during shore cleanup activities. 

Direct observation and measurement of the fate of the vast majority of the estimated 200 million gallons of oil presents a considerable challenge. In some cases, the estimates used to calculate these percentages contain considerable uncertainty. Even assuming that approximately half of the oil has been removed from the Gulf ecosystem through direct recovery, burning, skimming, or evaporation, the fate of the remaining (“other”) oil is unknown.

A complete and definitive answer to the question of the remaining oil is unknown at this juncture. It is debatable whether the fate of the remaining oil will ever be established conclusively, because multiple challenges hinder this objective: the complexity of the Gulf system; resources required to collect data; and varied interpretations over the results and observations. Moreover, as time progresses, determining the fate of the oil will likely become more difficult. Regardless, the question of oil fate will likely be answered through an incremental process. Researchers are continuing to study various components of the Gulf, specifically damages to natural resources. Some of these efforts may provide clues to the oil’s fate.

Because evaluating the actual fate of the oil may take time and may prove difficult, perceptions of the oil’s fate may influence congressional interest and action, with consequences for the affected stakeholders. The perception of the spill’s fate may be influenced by multiple factors, including oil spill assessments, the group that prepared the assessment, and the manner in which the assessment is presented. If policymakers have the perception that the oil has degraded with minimal impacts to the environment, attention to the oil spill’s consequences and associated impacts may wane. On the other hand, a perception that a substantial volume of oil remains and poses a threat to the environment could result in continuing pressure on Gulf industries and livelihoods.

Date of Report: December 16, 2010
Number of Pages: 24-
Order Number: R41531
Price: $29.95

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