How to control ship-to-ship transfer risk under OFAC

A cargo vessel sits at anchor off a coastal waypoint. Its AIS signal has been intermittent for three days. A second vessel moves alongside. Bunkers – or something else – are transferred. The chartering business that booked the cargo for the next leg has no knowledge of the event. That ignorance is not a legal shield. Under OFAC's sanctions regime, a party that facilitates a prohibited transaction can bear full liability even when the physical transfer happened at sea, out of sight, and apparently outside its control. Ship-to-ship transfer risk controls are not a maritime technicality. They are a sanctions compliance obligation.

Controlling ship-to-ship transfer risk under OFAC means building a documented, repeatable process that covers vessel identification, AIS monitoring, ownership and operator screening, cargo verification, and contractual protections – before each leg of a voyage and at each point of transfer. OFAC's rules on facilitation and the 50 percent rule (treating entities owned 50 percent or more by blocked persons as themselves blocked) apply to the chartering chain, the cargo financier, and the port agent, not only to the vessel owner. As of January 2026, OFAC's maritime enforcement posture continues to treat AIS manipulation and undisclosed ship-to-ship transfers as strong indicators of intentional sanctions evasion – a factor that bears directly on the egregious/non-egregious classification in its Enforcement Guidelines.

This guide walks through the key decision points for a cross-border business managing ship-to-ship transfer risk under OFAC, with comparisons to the OFSI and EU positions where the analysis diverges.

If you are assessing a voyage before it starts: what does your pre-fixture screen need to cover?

Before a fixture is confirmed, the minimum screen covers the vessel, the registered owner, the technical manager, the commercial operator, and any identified charterers – each run against the SDN List (OFAC's list of Specially Designated Nationals and blocked persons) and, where relevant, other OFAC-administered lists. Name screening alone is not sufficient. The 50 percent rule means that a company not itself listed may still be blocked because its ultimate beneficial owner is.

Start with the IMO number. Vessel names change; flags of convenience rotate; the IMO number follows the hull. Cross-reference the IMO number against OFAC's vessel designations. Then pull the ownership chain. In our experience, the critical gap in pre-fixture screening is the second and third ownership layer: a listed person with a 50 percent or more stake held through two intermediate holding companies is as fully blocked as a directly listed vessel. Screening tools that surface only the first registered owner miss this entirely.

Check the intended voyage route. A routing that passes through or near a jurisdiction subject to comprehensive OFAC restrictions raises the analysis immediately. So does a fixture where the load port or discharge port is in or adjacent to a territory under a territorial programme. Even a bunkering call at a designated port can create facilitation exposure for the charterer. The route check is not optional and should be documented.

At this stage the question to ask is simple: does anything in the vessel, ownership, or routing picture require a hold? If yes, stop and seek legal advice before proceeding. If the screen is clean, record it. The record is evidence of a functioning control.

If your vessel or counterparty has an AIS anomaly: how do you decide whether to proceed?

An AIS anomaly is any unexplained gap, manipulation, or inconsistency in a vessel's Automatic Identification System transmissions – including dark periods, spoofed positions, or transmissions that conflict with satellite imagery or port records. OFAC and partner regulators treat AIS anomalies as a primary red flag for maritime sanctions evasion.

The decision logic is a branch: the nature and context of the anomaly determines the next action.

Short, explainable dark periods in known traffic-dense anchorages, supported by independent voyage-data confirmation, may be resolvable through enhanced due diligence. A demand for voyage records, cargo manifests, and independent satellite confirmation from the vessel operator is the minimum response. You should also ask the operator directly for an explanation in writing. Document the response – or the absence of one.

Extended dark periods, especially in waters associated with sanctions evasion activity, are a materially different situation. In our practice, an unexplained AIS gap of more than 24 hours in a high-risk area, or any position discrepancy between the vessel's own transmissions and satellite imagery, is treated as a presumptive red flag that requires legal review before the voyage proceeds. Do not rely on the counterparty's oral assurance alone.

If the anomaly appears after a fixture has been confirmed, the question becomes whether the fixture can lawfully continue. That analysis turns on whether a prohibited ship-to-ship transfer has already occurred, whether blocked cargo has entered the supply chain, and whether continued performance would constitute facilitation. These are questions for sanctions counsel, not for the operations desk.

The cross-regime point matters here. Under OFSI and the relevant EU Council regulations, AIS manipulation is similarly treated as a diversion indicator. The EU's anti-circumvention instrument has extended the analytical reach further. A vessel that cleared a UK or EU screen at the time of fixture but subsequently develops AIS anomalies does not thereby become compliant with OFAC rules. Each regime's analysis is independent. Where two regimes both apply, the stricter prohibition governs – and in maritime matters, OFAC's extraterritorial reach is typically the widest.

For practical guidance on AIS anomaly indicators as they apply under EU monitoring obligations, see our related service on AIS anomaly indicators and EU sanctions diligence.

If a ship-to-ship transfer has already occurred: what must you establish first?

The first task is factual. Before any legal or commercial decision, you need to establish what actually happened – not what the bill of lading or the broker's summary says happened, but what satellite imagery, port records, AIS data, and cargo documentation show. This is the starting point for any OFAC exposure analysis, and it shapes every downstream decision.

The key questions are: What cargo was transferred? Between which vessels? At what location? Who were the beneficial owners of both vessels at the time of the transfer? Was either vessel, owner, operator, or charterer on the SDN List or subject to the 50 percent rule? Was the cargo itself subject to a sectoral, commodities, or list-based prohibition?

In our experience, the answers to these questions are rarely fully available at the moment of discovery. The operational team knows where the vessel last reported. The legal team knows what the charter party says. Neither knows the full ownership chain of the vessel that came alongside. Closing that information gap quickly – through maritime intelligence, shipping-registry searches, and direct inquiry – is the first operational priority.

If the evidence supports a conclusion that a prohibited transfer has occurred, two further questions arise immediately. First, does OFAC's blocked-property reporting obligation apply? A US person (or any person with US nexus) that has identified blocked property is required to report it to OFAC within 10 business days. That clock runs from the moment of knowledge or reason to know. Second, is there a voluntary self-disclosure obligation or opportunity? OFAC's Enforcement Guidelines treat voluntary self-disclosure as a mitigating factor. Early disclosure generally produces a better outcome than a disclosure that follows an investigation.

Records must be kept. OFAC's sanctions record-keeping obligation requires documentation to be retained for five years. Any internal investigation records, correspondence with the counterparty, and screening outputs from this point forward are potentially relevant documents.

How to control ship-to-ship transfer risk controls under OFAC: a step-by-step compliance checklist

The following sequence represents the minimum control architecture for a chartering, trading, or financing business with exposure to maritime sanctions risk. It is designed to function as a ship-to-ship transfer risk controls compliance checklist for recurring application – not a one-time exercise.

Step 1 – Vessel and ownership screen (pre-fixture). Screen the vessel by IMO number, the registered owner, the technical and commercial operator, and any identified sub-charterers against the SDN List. Map the ownership chain to the ultimate beneficial owner. Apply the 50 percent rule at each layer. Document the result and the date. Repeat the screen if the fixture is not executed within a defined number of days.

Step 2 – Route and cargo review (pre-fixture). Identify all planned waypoints, anchorages, bunkering stops, and load and discharge ports. Flag any port, territory, or routing segment subject to OFAC prohibitions. Confirm the commodity. Check whether the cargo is subject to a sectoral or thematic prohibition under the applicable OFAC programme.

Step 3 – Contractual protections (pre-fixture). Include sanctions warranties in the charter party or voyage contract. The warranty should cover the vessel, the owner, the operator, the cargo, and the destination. It should give the charterer a right to terminate without penalty if a sanctions concern arises. It should also require the counterparty to notify of any ownership change or AIS event during the voyage. Without these provisions, the chartering party's remedies are limited if a problem emerges mid-voyage.

Step 4 – Ongoing AIS monitoring (during the voyage). Monitor the vessel's AIS transmissions for the duration of the voyage. Set thresholds for escalation – for example, a dark period beyond a defined duration, or a position discrepancy above a defined margin. Use satellite-based vessel-tracking tools to cross-check AIS against independent imagery. Document the monitoring and any anomalies.

Step 5 – Mid-voyage screen refresh (on any anomaly or change). If an AIS anomaly occurs, or if the voyage route changes materially, repeat the vessel and ownership screen. Trade patterns and ownership structures can change during a voyage. A vessel that was clean at fixture may not be clean at discharge.

Step 6 – Post-voyage documentation. Retain all screening records, voyage documentation, AIS data, and any communications about anomalies or concerns. OFAC's five-year record-keeping obligation applies. Treat this as evidence that the compliance programme functioned – because in an enforcement context, it is.

What makes a ship-to-ship transfer situation materially worse?

Several actions – or inactions – consistently worsen a ship-to-ship exposure under OFAC. Identifying them is as important as the affirmative steps above.

Proceeding without a screen is the most common starting failure. A chartering business that executes a fixture without a documented pre-fixture screen has no evidence of good faith. OFAC's Enforcement Guidelines distinguish between parties that had a functioning compliance programme and parties that had none. The absence of a screen is not neutral: it weighs against the party in the egregious/non-egregious determination.

Relying on the seller's or broker's representations without independent verification is a distinct risk. This is one of the most persistent myths in maritime trade: that the seller's warranties and representations transfer, or remove, the buyer's sanctions exposure. They do not. OFAC's strict civil liability standard means that a party that conducts a prohibited transaction is liable whether or not it relied on a counterparty's assurance. The representations may give rise to a contractual claim against the other party. They do not provide a defence to OFAC. Independent verification is the only real mitigation.

Continuing a voyage after an unresolved AIS anomaly is a high-risk decision. If a dark period cannot be satisfactorily explained and the voyage proceeds anyway, that decision will be scrutinised in any subsequent enforcement review. The question OFAC will ask is what the party knew, when it knew it, and what it did. Continuing without escalation and legal review is a difficult position to defend.

Delaying a blocked-property report is serious. Once a US person (or a person with US nexus) has knowledge or reason to know that blocked property has been identified, the 10-business-day reporting clock runs. Missing that deadline is itself a violation.

How does OFAC's approach compare to OFSI and the EU?

The three major Western regimes share a common concern with maritime evasion, but their rules operate differently and a cross-border business needs to understand each.

OFAC's reach is the widest. It applies to US persons, US dollar transactions, and to any transaction that touches the US financial system. Secondary-sanctions risk can extend exposure to non-US parties that facilitate prohibited dealings. For maritime transactions routed through US dollar correspondent networks – which covers most commodity trades – OFAC's analysis is inescapable. The 50 percent rule is mechanical: the number triggers the status, regardless of intent. OFAC's facilitation prohibition catches a wide range of parties in the chartering and financing chain.

OFSI, operating under SAMLA and the relevant UK thematic regulations, applies a combined ownership-and-control test. An entity that a designated person controls – even without reaching the 50 percent or more ownership threshold – may still be caught. UK legislation has moved to strict-liability civil penalties for financial-sanctions breaches, with the maximum penalty set at the greater of £1,000,000 or 50 percent of the breach value (as currently in force, verify the current position before relying on it). OFSI requires relevant firms to report knowledge or suspicion of designated persons. The reporting obligation is not optional for entities within its scope.

The EU regime, established through Council Regulations, has an asset-freeze prohibition that extends to making funds or economic resources available, directly or indirectly, to or for the benefit of listed persons. In maritime terms, this can catch a charterer that pays freight to an operator whose ultimate beneficial owner is designated. The EU General Court provides a route for annulment challenges to listings; UK judicial review of designations runs to the High Court. The EU has applied anti-circumvention provisions to transit and rerouting, treating sharp changes in trade flows to third-country transit points as diversion red flags. A transit through a third country does not change an item's controlled status: origin and end-use analysis follows the cargo, not the route.

For the SECO position on ship-to-ship transfers under Swiss law, see our related guide on ship-to-ship transfer risk controls under SECO. For the diversion and rerouting analysis under Canadian rules, see our guide on transit and rerouting red flags under Canada's sanctions regime.

When should you involve sanctions counsel?

Some situations require legal advice; others benefit from it earlier than most businesses seek it. Knowing which is which prevents a resolvable situation from becoming a enforcement matter.

Seek counsel before proceeding when: (a) the pre-fixture screen produces any hit or near-match on the SDN List or the 50 percent rule analysis is inconclusive; (b) the AIS monitoring produces an unexplained anomaly and the counterparty cannot provide a satisfactory documented explanation; (c) the voyage route includes any segment in or adjacent to a territory subject to OFAC comprehensive sanctions; or (d) the cargo commodity is potentially within scope of a sectoral or thematic prohibition.

Seek counsel immediately when: a ship-to-ship transfer has already occurred without a prior screen; a screen run after the event produces a match; blocked property may have been identified; or an AIS gap is discovered that corresponds to a transfer event. In these situations, the 10-business-day reporting clock may already be running. Each decision in the following hours can affect the ultimate outcome.

We act for multinationals, financial institutions, and exporters on sanctions and export-control matters across the major regimes. We regularly advise on pre-fixture screening, AIS anomaly analysis, blocked-property reporting, and voluntary self-disclosure in maritime contexts. The Calder & Vance team can assess your exposure, advise on reporting obligations, and prepare any necessary OFAC submissions. Contact us at info@caldervance.com.

This publication is general information and does not constitute legal advice. For advice on your situation, contact info@caldervance.com.