On April 20, 2010, an explosion occurred on the Deepwater Horizon drilling platform in the Gulf of Mexico. The explosion, which killed 11 men, caused the rig to sink and started a catastrophic oil leak from the well. Before it was capped three months later, approximately 134 million gallons of oil had spilled into the Gulf, the largest offshore oil spill in U.S. history. Through the Natural Resource Damage Assessment (NRDA), we evaluated the type and amount of restoration needed in order to return the Gulf to the condition it would have been in before the spill and to compensate the public for the natural resource services that were injured or lost. The Deepwater Horizon spill resulted in the largest natural resource damage assessment ever undertaken.