Why the straits matter
The Danish Straits join the Baltic Sea to the North Sea through the Kattegat and the Skagerrak. According to Reuters, they are the main sea route in and out of the Baltic for commercial and military shipping.
According to the US Energy Information Administration (EIA), an average of 4.9 million barrels of oil a day passed through the straits in 2024. The same volume passed in the first half of 2025: 6% of world maritime oil trade and almost 60% more than in 2021. The EIA puts this growth down to the shift in trade flows from Russia.
According to the EIA, Russia was the largest oil exporter through the straits in the first half of 2025, and most of its volumes went from the Baltic to Asia and Turkey. From 2022, shipments from the US, Norway, the UK and Egypt to countries east of the straits, such as Poland and Finland, rose.
How the straits are laid out
There are three main straits: the Great Belt and the Little Belt in Danish territorial waters, and the Øresund (the Sound) between Denmark and Sweden. The Great Belt runs for about 60 km and is 16–32 km wide. The Øresund is about 118 km long and about 4 km wide at its narrowest, between Helsingør and Helsingborg.
Denmark set up Route T, a transit route for large ships, from Skagen through the Great Belt to the area northeast of Gedser. The maximum obtainable depth on most of the route is 17 m, and 16.4 m northeast of Gedser. According to the IMO, sea level changes, sand movement and unknown obstructions on the seabed can reduce the depth by up to 2 m.
The East Bridge spans the Great Belt; it opened to road traffic in 1998. Only part of its span over the shipping lane has a clearance of 65 m, and ships with an air draught of more than 64 m must pass nearer the centre of the lane. The Øresund Bridge opened over the strait in 2000.
Rules of passage
The Copenhagen Convention of 1857 abolished the Sound Dues and opened the straits to commercial ships with no charge for passage. It does not cover warships.
In the Great Belt, ships of 50 GT and above and ships with an air draught of 15 m or more must report to the vessel traffic service (VTS); in the Øresund, ships of 300 GT and above. Both services are staffed around the clock.
The IMO recommends that ships with a draught of 11 m or more take a pilot on Route T from Skagen to Gedser. The Danish authorities report breaches of this recommendation to the flag state. Under Danish law a pilot is compulsory in Danish waters for ships carrying oil, chemicals, gases or highly radioactive material and for ships with more than 5,000 t of bunker oil on board. The Danish Maritime Authority says a pilot is not compulsory for a ship in innocent passage.
Events since 2022
- February 2022. Russia began its full-scale invasion of Ukraine. According to the EIA, oil trade flows through the straits shifted after this and after the EU sanctions.
- December 2024. A group of 12 European countries agreed to act against tankers suspected of moving Russian oil around sanctions. The maritime authorities of the UK, Denmark, Sweden, Poland, Finland and Estonia agreed to ask such ships for proof of insurance as they passed through the English Channel, the Danish Straits, the Øresund and the Gulf of Finland. According to Bloomberg, there was no immediate penalty for refusing.
- February 2025. The Danish Maritime Authority began checking ships at the Skagen Red anchorage, tankers first, citing the risks from older ships carrying oil through the straits.
- October 2025. Denmark extended the Skagen checks to environmental rules: waste, ship recycling certificates, ballast water, scrubber discharge and fuel. According to gCaptain, sensors on the bridge over the Great Belt were to measure the sulphur content of ship fuel until the end of the year.
- October 2025. Denmark's intelligence service said Russian warships had repeatedly sailed on collision courses with Danish vessels in the straits and had aimed radars and weapons at Danish helicopters and ships.
- February 2026. The Danish Maritime Authority reported that tankers on the EU sanctions list made 292 voyages in Danish waters in 2025. The same month Swedish forces jammed a drone in the Øresund that was flying towards Malmö, where a French aircraft carrier was at anchor. Sweden said the drone had taken off from a Russian vessel; Russia denied this.
- September 2026. Denmark's defence command said a Russian frigate fired two flares towards a Danish military helicopter that was photographing it in international waters. Denmark summoned Russia's ambassador, who blamed the helicopter's dangerous manoeuvres. According to Reuters, Russia has dismissed accusations over such incidents.
Ship traffic
IMF PortWatch counts cargo ships and tankers from AIS signals. Of the Danish Straits, only the Øresund is on its list. The Great Belt and Route T are not in this count. According to its data, an average of about 54 such ships a day passed through the Øresund in 2019, about 45 in 2023 and about 47 in 2025, about 12 of them tankers.
What the map shows
The map opens on the Great Belt, at the East Bridge; on a phone the Øresund is out of view. To see the Skagen anchorage, zoom out. The rules for ships are collected in the Danish Emergency Management Agency's guide "Navigation Through Danish Waters".