The Protocol of 1978 relating to the International Convention for the Prevention of Pollution from Ships, 1973 (MARPOL 73/78), was adopted to “achieve the complete elimination of intentional pollution of the marine environment by oil … and the minimization of accidental discharge of [oil].” Parties to MARPOL believed this goal could best be achieved by the adoption of an international regime with specific operational and structural requirements for vessels and a comprehensive scheme for the detection and enforcement of violations. MARPOL, together with the United Nations Convention on the Law of the Sea, explicitly allocates enforcement among flag, port and coastal states. In recent years, port and coastal states, including the United States, have begun to look beyond MARPOL to domestic law to enforce MARPOL requirements on foreign flag vessels that (1) are suspected of MARPOL violations outside their jurisdiction but voluntarily enter their ports and (2) violate MARPOL while navigating in their coastal waters. The justification often given for more aggressive port state enforcement is inadequate flag state enforcement. Because of this perception, port and coastal states are assuming more enforcement responsibility. The impact of this upon the carefully negotiated international regime could be significant. This scheme, which reflects traditional international law and has been codified in both MARPOL and the Law of the Sea Convention, is at risk. This paper examines the international scheme and recent initiatives that threaten the scheme, and proposes actions to be taken at the international level to address the problems that have resulted in this trend toward less flag state enforcement and to strengthen the relevant international treaties to greater protect the marine environment.