On April 20, 2010, the Deepwater Horizon drilling rig exploded in the Gulf of Mexico resulting in 11 deaths, serious injuries, and the largest marine oil spill in U.S. history. Interior, which oversees offshore oil and gas activities, initiated a number of reforms following the incident to improve its oversight. This report assesses (1) Interior’s reorganization of its oversight of offshore oil and gas activities; (2) how key policy changes Interior has implemented since this incident have affected Interior’s environmental analyses, plan reviews, and drilling permit reviews; (3) the extent to which Interior’s inspections of drilling rigs and production platforms in the Gulf identify violations or result in civil penalty assessments; (4) when stakeholders provided input to Interior on proposed oil and gas activities, and the extent which they believe Interior considered their concerns; and (5) key challenges, if any, Interior faces in overseeing offshore oil and gas activities in the Gulf. GAO analyzed data and documents and interviewed officials from Interior and the Department of Commerce’s National Oceanic and Atmospheric Administration, Gulf of Mexico states, environmental groups, and industry.