We ran every OFAC-designated vessel through the same flag-jurisdiction classifier our vessel dossiers use. The 2.3% figure is the headline. The decomposition by sanctioned-state flags, shell registries, and the falsified-flag tail is the substance.
Source: US Treasury OFAC Specially Designated Nationals (SDN) list as of 19 May 2026 — SDN.CSV from sanctionslistservice.ofac.treas.gov.
Methodology: Each designated vessel is bucketed by flag jurisdiction using jurisdiction-tiers.ts — the same classifier used by ArcNautical's vessel dossier product. Tier 1 = EU member, UK, Norway, Iceland (public beneficial-ownership register). Tier 3 = classic flag-of-convenience / tax-haven registry. Sanctioned-state = state-instrument flag of a comprehensively sanctioned country. Other/unclassified = everything else (typically smaller intermediate jurisdictions).
Tonnage caveat: OFAC records usable tonnage for under 4% of designated vessels, so this Brief is reported by vessel count, not by tonnage. Tonnage-weighting would be computed on an unrepresentative ~4% sample and is deliberately not used.
Reproduce: re-pull SDN.CSV from the source URL above and re-run scripts/dark-fleet-flag-brief.ts from the ArcNautical repo. The dataset linked above carries full provenance.
Contact: Madhav · [email protected] — happy to discuss methodology or share the underlying calculation.