Ship-to-ship transfer techniques

Ship-to-ship (STS) transfer techniques are the operational methods for moving cargo, above all crude oil and refined products, between vessels at sea or at anchorage rather than in port. A routine commercial practice in bulk shipping, STS became the signature laundering mechanism of modern sanctions evasion: transferring cargo between vessels breaks the documentary and observational chain linking a cargo to its sanctioned origin.

Function

A typical evasion STS pairs a vessel that loaded in a sanctioned jurisdiction with a receiving vessel of cleaner profile, often at a permissive anchorage or in international waters. Supporting techniques include switching off or manipulating transponders (going dark), falsified bills of lading and certificates of origin, cargo blending to obscure provenance, floating storage to decouple loading from delivery, and rapid changes of vessel name, flag, and ownership through flags of convenience. Night transfers and multi-leg relays further degrade attribution.

Strategic significance

STS can interrupt the documentary chain between loading and discharge, but a transfer is not evidence of evasion on its own. Security Council resolution 2375 of 11 September 2017 requires states to prohibit specified transfers involving DPRK-flagged vessels. The Panel of Experts' 2024 report documented observed practices through dated imagery and tracking evidence. The Panel's mandate ended in April 2024 after the Security Council failed to renew it; the underlying resolutions remained in force. UK price-cap maritime guidance, checked on 30 July 2026, treats STS history, ownership, insurance and voyage documentation as risk indicators requiring due diligence, not as automatic proof of breach. The same distinction applies to reported transfers involving the shadow fleet and the Oil price cap.

Control or weaponisation history

Counter-STS enforcement fuses commercial satellite imagery, AIS analytics, and port-state measures against vessels with STS histories; designations of individual tankers made vessel identity itself a sanctions object. The countermeasure race is unresolved: analysts disagree on what fraction of sanctioned oil flows enforcement actually deters, given the elasticity of vessel supply and permissive registries.

See also

Russian oil-trade shadow fleet under post-2022 price-cap controls (2022-present) · AIS spoofing and GNSS manipulation ("going dark") · Ship registries and flags of convenience · Oil price cap · Economic statecraft

Sources

• Security Council Resolution 2375
• 2024 DPRK Panel report
• UK oil-price-cap maritime guidance
• IMO oil-pollution and transfer framework