The document discusses how NEPA analyses of offshore oil drilling programs treated risks and uncertainty prior to the 2010 BP Gulf oil spill. It notes that earlier NEPA tiers did not adequately incorporate new information into later analyses, and that risks of low-probability, high-impact events like catastrophic spills were not fully addressed. As a result, responses to the actual spill had to be developed hastily without sufficient prior planning. It examines approaches to addressing uncertainty under NEPA and calls for learning lessons to improve future risk evaluations.