Heterogeneities among states, among non-state actors and between state and non-state actors explain the timing, process, form and effectiveness of international regulation of intentional oil pollution. Understanding the progressive movement toward rules that reduced intentional oil discharges depends on identifying different varieties of heterogeneity and their unique influences on the process and outcomes of cooperation. Success at reducing discharges by tanker operators, who had few incentives to provide the public good of a cleaner ocean, depended on rules that took advantage of existing heterogeneities in preferences and capacities to build a regulatory structure that coerced compliance by preventing most violations and deterring the rest.