This paper provides estimates of the cost of preventing land-based plastic leakage into the ocean, covering 38 OECD member countries and 10 selected major plastic waste emitters in Asia and Africa. The study estimates capital costs at EUR 54 billion in the Moderate Ambition scenario and EUR 74 billion in the High Ambition scenario. The annualised per-capita costs range between EUR 0.2 to 6.5 in the Moderate Ambition scenario and from EUR 0.8 to 6.5 in the High Ambition scenario. These cost estimates are much lower than UNEP and ISWA estimates of the cost of inaction of inadequate waste management, roughly USD 9 to 45 per capita. Differences in estimated costs are found to depend on countries’ waste policy stringency and waste management infrastructure. This paper contributes to OECD work in support of a sustainable ocean economy and the Global Plastics Outlook report.