The Deepwater Horizon blowout has important lessons to teach about environmental review. It is easy to scapegoat the former Minerals Management Service (MMS) for shoddy environmental analysis. But captive agencies are a common phenomenon. Oversight by environmental mission agencies is supposed to provide a check on their myopia. Several external reviews of MMS’s environmental analysis were conducted, but none uncovered MMS’s wildly incorrect estimates of the probability, magnitude, and consequences of a blowout. This article details the external reviews, explains why they proved ineffective, and offers suggestions for improvement. Outside review cannot be effective unless reviewers understand the importance of their task, are able to focus on the key aspects of analyses they are reviewing, and can bring the appropriate expertise to bear. All of these elements were missing in reviews of the analysis that preceded drilling in the Macondo prospect. Their availability for future reviews would be improved if the executive branch took some relatively easy unilateral steps.