Ukrainian grain at a crossroads: the strategic importance of the Lower Danube in wartime

Russia’s full-scale invasion of Ukraine in 2022 disrupted exports through Ukrainian deep-water ports, increasing the importance of Danube ports in the country’s export system. The Black Sea Grain Initiative came to an end in July 2023, and a month later Ukraine opened its own maritime corridor. This allowed exports through its Black Sea ports to resume gradually. Yet the Lower Danube retained its importance as an alternative export route.

As recently as June 2026, according to the European Commission, around 90 per cent of Ukraine’s exports of cereals, oilseeds and related products passed through its Black Sea ports. The remaining ten per cent used the EU’s Solidarity Lanes. Just two months later, these proportions had reversed: in August, around 90 per cent of exports in this product group used the Solidarity Lanes and only ten per cent passed through the Black Sea ports. The October attacks on merchant vessels near the Romanian and Bulgarian coasts, followed by reports of further strikes on ships in the Black Sea in November, once again showed how quickly military threats can affect the safety of shipping.

Three routes from one port

The starting point is Izmail, a Ukrainian port on the Danube. Maize and wheat, Ukraine’s main grain exports, can be shipped directly from here by river–sea vessels known as coasters through the Ukrainian Bystre Canal or Romania’s Sulina branch. The third route involves barge transport to Constanța via the Danube and the Danube–Black Sea Canal. At the Romanian port, the grain is transhipped and consolidated before continuing aboard a larger ocean-going bulk carrier.

Constanța has a seemingly straightforward advantage: an ocean-going bulk carrier can carry far more grain than a coaster. The economies of scale, however, arise on the sea leg. They must be weighed against the cost of barge transport and the additional transhipment in Constanța. The direct routes do not require these operations. What matters, therefore, is not the cost of chartering a single vessel, but expenditure on the entire transport chain.

The model comparison covered maize and wheat, 13 destination ports on the Black Sea and the Mediterranean, shipments of 3,000 to 100,000 tonnes, and three hydrological scenarios. It accounted for vessel characteristics, port constraints, transhipment and a scenario-based component for additional war risk. The calculations cover transport from loading in Izmail to arrival at the destination port, excluding carriage of the grain to Izmail and discharge at the importer’s port. The results do not describe exporters’ actual choices. Instead, they identify the cheapest configurations under the adopted assumptions.

Why Sulina wins

The result is clear. Across the baseline grid of 302,718 combinations, Sulina was the cheapest option in 95.13 per cent of cases, Constanța in 3.40 per cent, and Bystre in 1.47 per cent. These figures are not actual export shares, but the percentages of cases in which each option was cheapest, irrespective of shipment size. Weighting these selections by shipment size raises Constanța’s share from 3.40 to 3.79 per cent.

What explains Sulina’s advantage? Navigation conditions play an important role. The deeper fairway along the Sulina branch allows larger vessels to be used. The model assigns this route a coaster with a reference cargo capacity of 5,800 tonnes, compared with 3,700 tonnes for the vessel on the shallower Bystre Canal. Under moderate navigational conditions, the allowable cargo mass per voyage is 5,220 and 2,960 tonnes, respectively. Although the smaller vessel is cheaper for an individual voyage, carrying the same grain shipment usually requires more voyages, which increases transport expenditure per tonne.

Sulina’s dominance does not mean it is the cheapest in every situation. Bystre gains an advantage within certain shipment size intervals, while Constanța does so for other combinations of shipment size and destination port. Bystre’s advantage is limited to relatively small shipments: in the baseline case, it is never the cheapest option on any route for shipments exceeding 18,500 tonnes.

When shipping via Constanța pays off

Constanța loses out when the benefits of cargo consolidation do not cover the cost of barge transport and transhipment. For smaller shipments, the direct routes are cheapest. In the baseline model, Constanța first gains an advantage for a shipment of 17,425 tonnes of wheat to Nador in Morocco under favourable navigational conditions on the Lower Danube.

The export destination matters. For Tarragona in Spain, Constanța is the cheapest route in 22.21 per cent of the combinations analysed for that port. For Nador, the corresponding figure is 16.49 per cent. For Alexandria (Egypt), Poti (Georgia) and Samsun (Turkey), it is never the most competitive option. A longer sea voyage offers more scope for economies of scale to offset the additional costs, but distance alone does not determine the result.

A comparison of three destination ports illustrates the importance of route length and port constraints. In the model, Alexandria and Tarragona permit the same bulk carrier classes and the same cargo masses per voyage. However, the route to Tarragona is around 1,437 kilometres longer. Constanța is not the cheapest option for Alexandria, whereas for Tarragona it gains an advantage across numerous shipment size intervals. For the even more distant Nador, however, port constraints rule out the two largest bulk carrier classes analysed, Panamax and Post-Panamax. Both distance and the receiving port’s technical characteristics therefore matter.

The trap of an extra 25 tonnes

The most surprising results are the abrupt jumps in expenditure. For 26,750 tonnes of wheat shipped to Nador under moderate water-level conditions on the Lower Danube, the cheapest plan via Constanța requires a single voyage by a Handysize bulk carrier. The entire chain then costs 39.77 euros per tonne, compared with 44.90 euros via Sulina.

Adding 25 tonnes takes the shipment beyond the cargo limit for a single Handysize voyage. The cheapest sea voyage plan therefore requires a larger Supramax. Expenditure on the Constanța route rises to 52.75 euros per tonne, while the Sulina figure is 44.87 euros. The jump in transport expenditure per tonne is not due to an increase in freight rates, but to the need to use a larger, more expensive bulk carrier and pay the full freight charge for the voyage, regardless of how fully the vessel is loaded.

Transport expenditure per tonne does not always decline smoothly as shipments grow. An additional voyage, a different bulk carrier class, or a port constraint can suddenly change the ranking of routes. There is therefore no single shipment size threshold above which Constanța becomes the cheapest option for all larger shipments.

The river changes the calculation

The Danube introduces another uncertainty: fluctuating water levels. At low water, vessels must reduce their loads, and pushed convoys comprise fewer barges, each carrying less cargo. The same shipment then requires more voyages. Improved navigational conditions do not, however, affect transport expenditure per tonne in the same way on all three routes.

The better the hydrological conditions on the Lower Danube, the more frequently the optimization model selected Constanța as the option that minimized total transport expenditure: for maize, from 0.42 per cent of cases at low water to 4.75 per cent under favourable conditions, and for wheat from 0.48 to 5.19 per cent. This does not mean, however, that improved navigational conditions always shift the boundaries of competitiveness in Constanța’s favour. Changes in water level have differing effects on the allowable cargo masses of coasters and pushed convoys. For pushed convoys, they also affect the number of barges.

War risk and route competitiveness

The model includes an additional surcharge for war risk in Izmail and on the initial section of the journey, examining how reducing or increasing it by half relative to the baseline affects the relative competitiveness of the transport options.

Across all three war-risk scenarios, Sulina remained the cheapest option in the vast majority of analysed cases. Increasing the surcharge had differing effects on the competitiveness of transport via Constanța: at low and moderate water levels on the Lower Danube, it reduced the number of cases in which this option was cheapest, whereas under favourable navigational conditions it increased that number. A higher surcharge increases transport expenditure for all three options. The size of this increase depends, among other factors, on the number of voyages needed to carry a given grain shipment, which in turn varies with hydrological conditions.

The strategic value of flexibility

Sulina’s dominance in terms of the exporter’s transport expenditure does not mean that the other routes lack an economic rationale. Bystre and Constanța retain advantages under certain conditions. Having different configurations available also broadens the scope for responding to changes in freight rates, hydrological conditions and war risk, strengthening the resilience of the transport system.

The findings also show the importance of Romanian transport infrastructure to the competitiveness of Ukrainian exports via the Lower Danube. Two of the three options examined use Romanian transport infrastructure: one follows the Tulcea section of the Danube and the Sulina branch to the Black Sea; the other uses the waterway connection to Constanța and the port’s transhipment infrastructure. Both can offer the lowest transport expenditure, but for different combinations of shipment size, destination port, and navigational conditions. The competitiveness of Ukrainian exports therefore depends in part on infrastructure on both sides of the border. Navigation coordination, efficient transhipment, and effective communication about transport constraints are important for the entire corridor.

The study does not account for delivery time, the availability of vessels with the required carrying capacity, congestion, or administrative restrictions on navigation. The results nevertheless suggest that planning investment in port infrastructure and waterways should take account not only of improvements to their technical characteristics, but also of the project’s effect on transport expenditure across the entire chain.

The war has increased the importance of alternative routes for Ukrainian grain exports. However, their availability alone does not determine whether transport is economically viable. The analysis shows that although transport via Sulina most often minimizes the exporter’s expenditure, Bystre and Constanța can also be competitive under certain conditions. The Lower Danube’s importance to Ukrainian exports therefore depends not only on how much grain can be shipped along it, but also on the conditions under which its individual routes allow transport expenditure to be reduced.

Adrian Sadłowski holds a doctorate in economics and is an assistant professor at the Institute of Economics and Finance at Cardinal Stefan Wyszyński University in Warsaw. His research focuses on agricultural policy, agri-food trade, and the logistics of agricultural products.