Danish Straits oil: the Baltic gate for Russia's shadow fleet

Danish Straits oil flows reached about 4.9 million barrels a day in the first half of 2025, according to the EIA, around 6% of world seaborne oil trade. The straits (the Great Belt, the Little Belt and the Øresund, reached through the Kattegat and Skagerrak) are the only sea route between the Baltic and the open ocean, so every tanker loading at Russia's Baltic terminals of Primorsk and Ust-Luga has to pass through them. Most of the oil crossing is Russian crude and products heading for India, China, Türkiye and the Mediterranean.

Since 2022 the straits have also become the main observation point for Russia's shadow fleet, the ageing tankers with opaque ownership and non-Western insurance used to move oil around Western sanctions. The Danish Maritime Authority counted 292 voyages by EU-sanctioned tankers in Danish waters in 2025, similar to 2023 and 2024. What Denmark cannot do is close the straits: the Copenhagen Convention of 1857 and the law of the sea guarantee free passage, so enforcement has taken the form of inspections and insurance checks rather than blockade.

Key numbers

What flows through the Danish Straits

Russian oil dominates. Primorsk and Ust-Luga are Russia's main Baltic export terminals for Urals crude, and St Petersburg and Ust-Luga load diesel, fuel oil and naphtha. Before 2022 most of these barrels went to northwest Europe; since the EU embargo they sail on to the Mediterranean, the Suez route or around Africa to India and China, which lengthens voyages but does not change the exit through Denmark. The rest of the flow is Baltic and North Sea trade: Scandinavian refinery products, Polish and Finnish imports, and bulk and container traffic of the Baltic states.

The deepest route is the Great Belt, which the largest tankers use. The Øresund, between Copenhagen and Malmö, is shallower and carries smaller ships. Under-keel limits keep the largest crude carriers out of the Baltic, so Russian crude leaves on Aframax and Suezmax tankers and is often transferred to larger ships further along.

Who depends on the Danish Straits

Russia depends on them most. The Baltic terminals are among its largest export outlets for crude and products, and there is no alternative sea route out of the Baltic. The buyers of Russian seaborne oil, above all India and China, depend on the same corridor for part of their supply. See Russia's seaborne crude exports.

The Baltic states, Finland, Poland and eastern Germany depend on the straits for their own seaborne trade, including LNG and crude imports that replaced Russian pipeline supply after 2022.

Alternatives and bypass routes

Kiel Canal. The German canal links the Baltic to the North Sea but takes only smaller ships; it is not an alternative for loaded Aframax and Suezmax tankers.

Other Russian ports. Russia can shift exports to the Black Sea through the Turkish Straits, to the Arctic port of Murmansk or to Kozmino on the Pacific, but each route has its own capacity and chokepoint.

Pipelines. Druzhba still sends some Russian crude to Central Europe, but the Baltic terminals were built precisely to replace pipeline transit, and no pipeline can take their volume.

Historical incidents

Assets and companies exposed

Russian exporters and terminals. Transneft's Primorsk and Ust-Luga terminals and the traders that move Russian crude and products, many of them registered outside Russia.

Shadow fleet operators. Ageing tankers with opaque ownership and non-Western insurance, the focus of Danish inspections and of EU and UK sanctions listings.

Coastal states. Denmark and Sweden carry the spill and collision risk of heavy tanker traffic in narrow waters, and pilots and rescue services on both sides are exposed to incidents involving uninsured ships.

Baltic importers. Refiners and LNG terminals in Poland, Finland, the Baltic states and Germany that depend on the same lanes. This entry is descriptive: the encyclopedia does not publish recommendations.

What to watch

• Danish Maritime Authority reports on sanctioned tanker voyages and inspections at Skagen.
• EU and UK sanctions listings of shadow fleet vessels.
• Russian Baltic loadings at Primorsk and Ust-Luga, tracked by Kpler and Vortexa.
• Seabed incidents involving cables or pipelines, and any change in the legal basis for boarding stateless tankers.

FAQ

How much oil passes through the Danish Straits? About 4.9 million barrels a day in the first half of 2025, according to the EIA, roughly 6% of world seaborne oil trade. Most of it is Russian crude and products from the Baltic ports of Primorsk and Ust-Luga.

Can Denmark block Russian tankers in the straits? No. The Copenhagen Convention of 1857, which abolished the Sound Dues, and the law of the sea guarantee free passage through the straits. Denmark instead inspects tankers that anchor off Skagen and are not in innocent passage, checks insurance and funds environmental inspections.

What is the shadow fleet? The ageing tankers with opaque ownership, frequent flag changes and non-Western insurance that carry Russian oil outside the G7 price cap and EU sanctions. Denmark recorded 292 voyages by EU-sanctioned tankers through its waters in 2025.

Is there an alternative to the Danish Straits for Russian oil? Not for Baltic exports. The Kiel Canal is too small for loaded tankers, and the only way out of the Baltic by sea is through Danish waters. Russia can export more through the Black Sea, the Arctic or the Pacific, but each route has limited capacity.