05.12.2025

Three Seas Initiative gas index – for enhancing regional gas cooperation

Three Seas Initiative (3SI) GAS INDEX
A new index concept for enhancing gas cooperation between Lithuania, Poland, Croatia, and Greece

The Three Seas region is rapidly expanding its LNG infrastructure. The terminals in Klaipėda, Świnoujście, Gdańsk, Krk, and Alexandroupolis now form the main supply corridor for natural gas into Central and South-Eastern Europe. Despite this growing infrastructure, regional gas markets continue to settle based on the Western European TTF index, which does not reflect the specific conditions or LNG-driven reality of the Three Seas region.

In response, the 3SI Gas Index is being developed as the first joint gas price index for the Three Seas countries. It represents a fast, pragmatic, and market-based step toward deeper energy integration. At the same time, it lays the foundation for a future common gas market built on data, transparency, and cross-border cooperation.

The 3SI Gas Index provides a regional gas price benchmark based on real transactions from four national markets. It uses a VWAP-type index model complemented by an infrastructure adjustment, operating similarly to TTF but adapted to the characteristics of LNG supply. The index draws on data from gas trading platforms (GET Baltic, TGE, CROPEX, HEnEx) as well as LNG terminals, ensuring that it reflects the actual cost of LNG deliveries to the region.

Introducing the 3SI Gas Index has significant implications for market development. It strengthens the region’s negotiating position with LNG suppliers and helps achieve more favorable contract conditions. It also enhances price transparency by relying on physical transactions rather than speculative signals. Moreover, it supports the emergence of a Three Seas financial market by enabling new instruments such as futures, forwards, options, and 3SI–TTF spreads.

Alongside the index, market swaps will be introduced to facilitate price swaps between national markets—for example between Poland and Lithuania, Poland and Croatia, or Poland and Greece. These instruments will allow companies to trade gas across the region without the need to harmonize domestic tariffs or regulatory frameworks.

Both companies and end-users will benefit from the 3SI Gas Index. It will help stabilise and better predict gas prices, enhance the competitiveness of supply, provide more advanced risk-management tools, and contribute to the real integration of gas markets across the Three Seas region.

Małgorzata Samojedny
Ireneusz Łazor