As Southeast Europe (SEE) transitions towards a more interconnected energy landscape, cross-border electricity flows are increasingly shaping market dynamics. By early 2026, the region will no longer operate as a collection of isolated national markets; instead, it will function as a semi-coupled network of corridors. This evolution is critical for understanding how price formation occurs, driven not only by local generation costs but also by interconnector availability and congestion patterns.
The shift from emergency balancing to continuous arbitrage marks a significant structural change in the region’s electricity markets. Between 2022 and 2024, political constraints and export limitations hampered cross-border flows. However, by 2026, many of these restrictions have been relaxed, allowing interconnectors to fulfill their primary economic role of transmitting price signals. Consequently, congestion rents have emerged as a substantial component of wholesale electricity economics in SEE.
Key corridors such as Hungary–Romania, Hungary–Serbia, Romania–Bulgaria, and Bulgaria–Greece have become essential for regional price transmission. These routes connect major trading hubs like HUPX, OPCOM, and IBEX to regions experiencing supply deficits or volatility. In areas where these borders are unconstrained, prices tend to align quickly; however, when constraints arise, price divergences can reach €20–40/MWh within the same delivery hour.
Hungary plays a pivotal role in this interconnected system due to its extensive network connections rather than being the lowest-cost market. During periods of surplus generation, power flows into Hungary from Romania and Slovakia, while during peak demand times, it exports to Serbia, Croatia, and Slovenia. This bidirectional flow on typical winter days illustrates Hungary’s role as an optimization node reflecting regional marginal values rather than solely domestic generation costs.
The Hungary–Serbia border is particularly crucial within the Western Balkans. Serbia’s internal market has developed sufficient liquidity to both absorb imports and export surplus energy. In January 2026, price spreads between Hungary and Serbia fluctuated between €5 and €15/MWh, especially widening during peak hours in Serbia. When cross-border capacity was fully utilized, these spreads narrowed rapidly; however, when constrained, Serbian prices decoupled significantly, leading to increased industrial procurement costs.
In contrast, the Romania–Hungary flows present a different scenario due to Romania’s diverse generation mix. This allows Romania to export consistently during various demand periods. As a result, it often stabilizes prices in Hungary during colder months by preventing spikes that could push day-ahead prices above €130/MWh.
The Romania–Bulgaria corridor has emerged as one of the most actively utilized borders in SEE. Both countries maintain strong baseload capacities—nuclear power in both cases—which facilitates consistent export capabilities. Congestion rents on this border typically range between €2 and €6/MWh during winter months. For traders, this represents low-risk arbitrage opportunities while providing industrial consumers with relatively stable pricing conditions.
The Bulgaria–Greece border presents a different challenge due to Greece’s reliance on gas for marginal pricing amid increasing renewable energy sources. This creates pronounced intraday price fluctuations that can lead to significant spreads exceeding €7–10/MWh during peak hours. Such conditions have resulted in higher delivered prices for Greek industrial consumers compared to their counterparts in Bulgaria or Romania by €8–15/MWh.
Further westward, the Serbia–Croatia and Croatia–Slovenia borders illustrate how hydro flexibility interacts with congestion issues. Croatia’s hydroelectric resources allow for dynamic exports; however, limited interconnector capacity can prevent access to high-value markets. Slovenia’s integration with Austria provides some relief but does not eliminate bottlenecks entirely. When congestion occurs, Croatian prices may diverge by €10–20/MWh from neighboring markets.
The ADEX framework linking HUPX, SEEPEX, and Slovenia’s market aims to mitigate these challenges by reducing friction in access to markets. Although it does not eliminate physical constraints entirely, it enhances the speed of price signal transmission among traders and reduces the duration of price divergence even when convergence is not feasible.
In the southern Western Balkans, cross-border flows remain less robust. Albania and Kosovo depend heavily on imports during dry seasons or low-hydro periods due to limited interconnector depth. Consequently, imports often occur at peak prices leading to sustained premiums against Bulgaria and Greece that can exceed €10/MWh during high-load hours.
Montenegro exemplifies extreme vulnerability with minimal liquidity on BELEN and restricted cross-border flexibility leading to significant price volatility. In January 2026 alone, prices ranged from below €50/MWh during surplus conditions to above €200/MWh when imports were limited—a situation that poses substantial risks for industrial consumers reliant on stable pricing.
The economic implications of cross-border flows are clear: markets experiencing over 25-30% congestion hours during peak times typically see an additional risk premium of €8-12/MWh for industrial consumers. Conversely, lower congestion hours correlate with reduced premiums around €3-5/MWh—this trend is observable across supply contract margins throughout SEE.
Trading companies such as Axpo and Statkraft play a vital role in optimizing these corridors by monetizing congestion while minimizing unjustified price spreads. Their operations ensure that borders function effectively as economic valves rather than barriers that inflate costs for consumers.
By early 2026, the hierarchy of cross-border electricity flows in SEE will be well-defined: Romania–Hungary and Romania–Bulgaria serve as stabilizing corridors; Bulgaria–Greece represents high-value volatility; Hungary–Serbia acts as the main transmission spine for the Western Balkans; while Croatia–Slovenia remains strategically important despite constraints. Albania, Kosovo, and Montenegro will continue to be peripheral until deeper market coupling occurs.
This evolving landscape indicates that competitiveness in SEE will increasingly depend on border accessibility and pricing transmission efficiency rather than solely on national generation costs. Without expanded cross-border capacity and enhanced integration among markets, geographical factors will persist as a cost burden reflected in euros per megawatt-hour throughout the year.
