The Deepwater Horizon accident is one of the major environmental disasters in the history of the United States. This accident occurred in 2010, when the Deepwater Horizon mobile offshore drilling unit exploded, while the rig's crew was conducting the drilling work of the exploratory well Macondo deep under the waters of the Gulf of Mexico. Environmental damages included more than four million barrels of oil spilled into the Gulf of Mexico, and economic losses total tens of billions of dollars. The accident brought into question the effectiveness of the regulatory regime for preventing accidents, and protecting the marine environment from oil and gas operations, and prompted regulatory reforms. Ten years after the Deepwater Horizon accident, this article analyzes the implementation of Safety and Environmental Management Systems (SEMS) as one of the main regulatory reforms introduced in the United States after the accident. The analysis uses the theory of regulation which takes into account both state and non-state actors involved in regulation, and therefore, the shift from regulation to governance. The study includes regulations issued after the Deepwater Horizon accident, particularly, SEMS rules I and II, and reports conducted by the National Academy of Sciences, the National Commission on the BP Oil Spill, the Center for Offshore Safety, the Chemical Safety and Hazard Investigation Board, and the Bureau of Safety and Environmental Enforcement (BSEE). The article reveals that though offshore oil and gas operators in the U.S. federal waters have adopted SEMS, as a mechanism of self-regulation, there is not clarity on how SEMS have been implemented in practice towards achieving its goal of reducing risks. The BSEE, as the public regulator has the task of providing a complete analysis on the results of the three audits to SEMS conducted by the operators and third parties from 2013 to 2019. This article argues that the assessment of SEMS audits should be complemented with leading and lagging indicators in the industry in order to identify how SEMS have influenced safety behavior beyond regulatory compliance. BSEE has the challenge of providing this assessment and making transparency a cornerstone of SEMS regulations. In this way, the lessons of the DHW accident may be internalized by all actors in the offshore oil and gas industry.