In the wake of the explosion of the Deepwater Horizon offshore drilling rig on April 20, 2010, federal agencies, state and local government agencies, and responsible parties faced an unprecedented challenge. Never before had a subsea drilling system discharge of this magnitude, or an oil spill of this size—estimated at approximately 206 million gallons (4.9 million barrels)—occurred in U.S. waters. The incident tested the public and private response capabilities, as well as the legal framework of liability and compensation under the Oil Pollution Act. The oil spill cleanup, natural resource damage assessment (NRDA), and compensation processes continue today. This report provides a summary update of selected issues related to the 2010 Deepwater Horizon oil spill: Oil spill response, Fate of the oil, Gulf Coast restoration, Economic claims and other payments, Civil and criminal settlements, Department of the Interior regulatory developments, Dispersant regulations, Congressional activity, and Investigations and reports. More detailed analysis of these and other issues is addressed in other CRS products, some of which are listed at the end of this report. The uncontrolled discharge from the Deepwater Horizon continued for approximately 87 days until, following several attempts, responders gained control of the release on July 15, 2010. The response involved multiple agencies. As this spill occurred in the coastal zone, an on-scene coordinator from the U.S. Coast Guard continues to direct and coordinate the on-site activities of federal, state, local, and private entities (e.g., BP and its contractors). This framework of multiple parties working together under the leadership of the federal government is referred to as the Unified Command. During the height of operations in the summer of 2010, response personnel levels reached 47,000, and response vessel numbers approached 7,000 ; and the maximum extent of shoreline oiling involved almost 1,100 miles of shoreline. Response activities specific to the 2010 incident have diminished substantially: In June 2013, the Coast Guard announced that the shorelines of Alabama, Florida, and Mississippi returned to the pre-spill reporting system via the National Response Center. In April 2014, the Coast Guard announced that Louisiana shoreline activities will transition to a "Middle Response" process, akin to the process in Alabama, Florida, and Mississippi. At that time, the federal on-scene coordinator stated that "this response is not over—not by a long shot. The transition to the Middle Response process does not end clean-up operations." In February 2015, a Coast Guard memorandum announced that in March 2015, the Gulf Coast Incident Management Team would "transition from Phase III (Operations) ... and reconstitute as a Phase IV Documentation Team." As part of that transition, Coast Guard field unit commanders would respond to reports of oil spills in their respective areas of responsibility. The local commanders are to use their discretion to decide if sampling is needed to identify the source of the oil (i.e., related to the Deepwater Horizon incident). As of April 2015, 30 response personnel, including federal officials and civilians, are working on activities related to the Deepwater Horizon incident. Following the containment of the Macondo well in July 2010, satellite data began to reveal decreasing daily quantities of oil on the ocean's surface. Many stakeholders wondered where the oil went. In November 2010, the federal government released a peer-reviewed publication that provided an estimate of what happened to the oil. The study concluded that approximately 50% of the oil had evaporated, dissolved, or been effectively removed from the Gulf environment through human activities. Thus, at the time of the study, a substantial portion—over 100 million gallons—remained, in some form, in the Gulf. Subsequent research has offered some insights into the fate of this "remaining" oil. Some research suggests that microbial organisms (bacteria) consumed a considerable amount of the oil in the water column. Other studies have found evidence indicating that a considerable amount of the oil settled on the sea floor. When a spill occurs, natural resource trustees conduct an NRDA to determine the extent of the harm. Trustees may include officials from federal agencies designated by the President, state agencies designated by the relevant governor, and representatives from tribal and foreign governments. Natural resource damages are intended to be compensatory, not punitive. Collected damages cannot be placed into the general treasury revenues of the federal or state government but must be used to restore or replace lost resources. The National Oceanic and Atmospheric Administration (NOAA) oversees the NRDA process. The trustees' work occurs in three steps: a pre-assessment phase, the restoration planning phase, and the restoration implementation phase. The Deepwater Horizon NRDA process is in the restoration planning phase. In 2011, BP agreed to provide $1 billion toward early restoration projects in the Gulf of Mexico to address injuries to natural resources caused by the spill. "Early restoration" projects may be developed prior to the completion of the injury assessment, which may take months or years to complete. Distribution of early restoration funds has been divided into three phases. The first two phases of early restoration, announced in 2012, were completed and resulted in 10 projects at an estimated cost of approximately $71 million. In May 2013, the trustees proposed additional projects under a third phase. The plan for these projects, finalized in June 2014, proposes funding an additional 44 early restoration projects at a cost of approximately $627 million. Thus, as of March 2015, the total funding allocated or spent on early restoration projects was $698 million for 54 projects. The funding for the early restoration projects will be credited against BP's liability for natural resource damages resulting from the spill. In addition to natural resource damages that were a direct result of the spill, the Deepwater Horizon incident generated interest in natural resource issues in the region that were present before the spill occurred. On June 15, 2010, the Administration committed to developing a long-term Gulf of Mexico restoration plan for post-spill recovery needs as well as long-term restoration. In contrast to the environmental damages addressed by NRDA, the Administration's plan would address a broader array of restoration needs, many of which predate the oil spill. To further this objective, the President established the Gulf Coast Ecosystem Restoration Task Force in October 2010 to develop a restoration strategy, which was released in December 2011. With the enactment of the RESTORE Act (discussed below) in July 2012 and the creation of the Gulf Coast Ecosystem Restoration Council, the President disbanded the task force. On July 6, 2012, the President signed P.L. 112-141 (MAP-21), which includes a subtitle referred to as the RESTORE Act. The RESTORE Act establishes the Gulf Coast Restoration Fund in the General Treasury. Eighty percent of any administrative and civil Clean Water Act (CWA) Section 311 penalties paid by responsible parties in connection with the 2010 Deepwater Horizon oil spill will provide the revenues for the trust fund. Amounts in the fund will be available for expenditure without further appropriation. The RESTORE Act distributes monies to various entities through multiple processes: 35% divided equally among the five Gulf of Mexico states to be applied toward one or more of 11 designated activities; 30% provided to a newly created Gulf Coast Ecosystem Restoration Council to finance ecosystem restoration activities in the Gulf Coast region; 30% disbursed by the council to the five Gulf states based on specific criteria: shoreline impact, oiled shoreline distance from the Deepwater Horizon rig, and coastal population. Each state must submit a plan for approval documenting how funding will support one or more of the 11 designated activities; and 5% to support marine research and related purposes. As a result of a CWA civil settlement with Transocean—the owner of the Deepwater Horizon drilling rig and an identified responsible party—a total of $800 million, plus interest, is expected to be deposited into the trust fund. Potential CWA civil penalties against BP, which could be considerable, are discussed below. Section 311 of the CWA authorizes certain civil judicial penalties for the owner, operator, or person in charge of a vessel, onshore facility, or offshore facility for violations of that provision. A civil judicial penalty applies to a violation of the CWA prohibition on discharging oil into navigable waters of the United States. The monetary penalty for this violation may be up to $37,500 per day of violation, or up to $1,100 per barrel discharged. If the violation is deemed a result of gross negligence or willful misconduct, the penalty is not less than $140,000 for the violation or more than $4,300 per barrel discharged. A federal judge for the Eastern District of Louisiana has issued rulings on two factors that may play a critical role in the ultimate penalty determination: the degree of negligence and the volume of the spilled oil. On September 4, 2014, the judge determined that, within the context of the civil penalty provisions, the discharge of oil in the 2010 Deepwater Horizon incident was the result of BP's "gross negligence" and "willful misconduct." BP has appealed this ruling. On January 15, 2015, the same judge determined that the oil spill resulted in a discharge of 3.19 million barrels (134 million gallons) of oil into the Gulf of Mexico. Reportedly, both BP and the Department of Justice have appealed or plan to appeal the judge's determination. Based on the January 2015 and September 2014 court decisions, the maximum potential CWA civil penalty that could be assessed to BP would be $13.7 billion—calculated by multiplying 3.19 million barrels by $4,300/barrel. By comparison, the penalty ceiling would likely be $3.5 billion if a court, through the appeals process, ultimately determines that the discharge was not a result of gross negligence or willful misconduct.