Oil from the Deepwater Horizon drilling rig explosion flowed into the Gulf of Mexico for 3 months in 2010 until it was successfully capped. It became the largest accidental marine oil spill in the history of the petroleum industry, releasing about 5 million barrels of crude oil and causing extensive damage to marine and wildlife habitats as well as the Gulf's fishing and tourism industries. Scientists also report immense underwater plumes of dispersed oil not visible at the surface. The spill’s impact will be profound and lasting. This session examines the various facets of this, including the likely causes of the disaster and the viability of prevention, or at least the amelioration of environmental damage from such disasters. The advisability of the use of dispersants, significance of the aforementioned plumes, effectiveness of bacterial degradation, and related matters will be debated. The consequences of the disaster will be viewed through the lenses of national policy, economics of alternatives, effect on the environment of alternatives, and other externalities related to the choices driven by policy.