BLM is responsible for managing oil and gas development on federal lands while mitigating related environmental impacts. BLM seeks to do so, in part, by applying requirements to the leases and drilling permits it issues to operators. These requirements may include environmental mitigation practices outlined in BLM's best management practices policy. In some cases, operators may request exceptions to lease and permit requirements. GAO was asked to examine BLM's efforts to mitigate environmental impacts from oil and gas development. This report examines the extent to which BLM (1) approved requests for exceptions to lease and permit requirements and how these decisions were made and documented, (2) involved the public in the development of lease and permit requirements and in the approval of exception requests, and (3) implemented and assessed the effectiveness of its best management practices policy. GAO examined laws, regulations, and BLM policies and documents; surveyed and visited BLM field offices; and conducted interviews with BLM officials and other stakeholders.