The Vertical Gas Corridor and Russian Influence on Bulgarian Gas Policy

The second and third routes of the Vertical Gas Corridor—through the Greece-Bulgaria interconnector and the Alexandroupolis LNG terminal—are intended to expand transmission capacity to Romania, Moldova, and Ukraine. Their purpose is to diversify regional supplies by channeling non-Russian gas from Greek and Turkish terminals, along with future LNG imports. Yet progress has stalled, casting doubt on Bulgaria’s commitment to energy diversification. Although we have examined this issue before, the persistent delays in developing these two routes warrant a fresh review.

Stagnation in Infrastructure Development

Despite a high-profile ceremony marking the launch of the first route and upgrades to the Sidirokastro–Kulata interconnection (see map), little progress has followed. The critical bottleneck—a missing 67 km pipeline between Rupcha and Vetrino, which could unlock an additional 13 billion cubic meters (bcm) per year of reverse flows through the Trans-Balkan Pipeline—remains unaddressed. Instead, Bulgartransgaz’s CEO has prioritized marginal expansions north of the Greek border.

Consequently, the Trans-Balkan system’s pipelines remain largely idle, while TurkStream maintains its dominance over regional gas flows. According to Bulgartransgaz’s website, the Kardam–Negru Voda 2 and 3 connections, with a combined capacity of over 13 bcm annually, show zero throughput. This represents Southeast Europe’s largest unused transmission capacity, capable of meeting demand in Moldova, Romania, and Ukraine.

In contrast, the older Kardam–Negru Voda 1 line, previously used for Gazprom deliveries to Bulgaria, now operates in reverse mode at near-full capacity. Daily “extra” gas flows have risen from 6 to nearly 15 million cubic meters (mcm), with nominations continuing to increase. This underscores the urgent need to activate the second and third Trans-Balkan pipelines, yet decisions are repeatedly delayed despite soaring seasonal demand.

Sources of Gas Flows

Although the Vertical Corridor is technically operational, only Route 1 (Sidirokastro–Kulata) delivers modest exports northward, insufficient to account for the ~15 mcm/day exiting Bulgaria toward Romania. A breakdown of entry flows into the Bulgarian gas transmission system reveals:

• Sidirokastro–Kulata (Greece): ~4 mcm/day, mostly backhaul – Russian gas – stable with no significant growth.
• IGB (Greece–Bulgaria Interconnector): ~2.5 mcm/day, fully absorbed by Bulgargaz’s Azeri contract.
• Strandzha (Turkey): ~4.5 mcm/day, primarily under SOCAR and Botas contracts.
• Strandzha 2 (TurkStream): ~50 mcm/day of Russian gas enters Bulgaria, with 26–28 mcm directed to Serbia and the remainder split among Greece, Bulgaria’s domestic market, Hungary, and Romania.

The data is clear: the bulk of increased flows to Romania and beyond stem almost entirely from Russian gas via TurkStream, not from Azeri supplies, American or other LNG from Greek and Turkish terminals.

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Causes of Inaction

The official explanation for the delay is the unbuilt Rupcha–Vetrino pipeline (see red dash line on both sides of Provadia on the map), critical for linking the Trans-Balkan system to Routes 2 and 3. However, this section of the original Trans-Balkan pipeline was effectively hijacked to serve the needs of TurkStream, which benefits Russian gas flows. While 484 km of TurkStream’s pipeline east of Nova Provadia was constructed across Bulgaria in just over a year to meet Moscow’s demands, no progress has been made on this essential infrastructure to support Ukraine.

Instead, Bulgartransgaz has focused on questionable domestic projects, such as loops after Petrich and further north that feed gas to power plants owned by a well-connected energy oligarch (e.g., TPP Bobov Dol, Toplofikatsia Pernik, and sites in the Maritsa basin). Additionally, the expansion of the Chiren gas storage facility—a vital project for balancing LNG and non-Russian imports—has faced endless delays since 2011.

This pattern suggests not bureaucratic inertia but a deliberate policy that perpetuates Russian gas dominance through prirotizing Russian gas flows via the TurkStream while limiting Ukraine’s access to alternative supplies via the Vertical Gas Corridor.

Geopolitical Implications

As Bulgaria stalls, Russia intensifies missile strikes on Ukraine’s energy infrastructure, targeting compressor stations and storage facilities to disrupt winter supplies. Ukraine’s best hope lies in the unused Trans-Balkan capacity, yet politically motivated delays in infrastructure upgrades undermine the EU’s strategy to eliminate reliance on Russian gas.

The situation is exacerbated by the “technical” outage of the Alexandroupolis LNG terminal, which strengthens Moscow’s grip on gas supplies. These developments highlight how Russian influence, enabled by its regional assets, continues to shape Bulgaria’s energy decisions.

The Vertical Gas Corridor is promoted as a flagship of diversification and energy independence. In reality, the data proves that it serves as a conduit for more Russian gas, notably with the refusal to activate the second and third Trans-Balkan pipelines. And this is a geopolitical choice with inaction entrenching TurkStream’s dominance, undermining Bulgaria’s energy security, and weakens Europe’s ability to support Ukraine through the coming winter.