ACER finds latest Slovak gas transmission tariff proposal not aligned with EU rules

Today, ACER releases its report on the Slovak gas transmission tariffs directed at Eustream, Slovakia’s transmission system operator (TSO).

The report assesses the compliance of the proposed reference price methodology (RPM) with the requirements of the EU Network Code on Harmonised Transmission Tariff Structures (NC TAR). 

Eustream had previously proposed the application of a new tariff methodology for January 2026 to December 2027, with indicative tariffs calculated for that period (see ACER analysis). In April, the Slovak energy regulator, ÚRSO, approved lower transmission tariffs than Eustream had proposed, to be applied from 1 May 2026. Following this decision, Eustream launched a new consultation on 30 June, proposing the same tariffs as in the previous consultation, with only minor methodological changes. 

On 8 October 2026, ÚRSO discontinued the tariff proposal procedure, which also ended the RPM proceeding. There is a 40-day period to appeal against ÚRSO’s decision. The discontinuation of the Slovak procedure does not affect ACER’s obligation to publish its analysis.

What is the proposed tariff methodology?

The Slovak TSO proposes to:

• Introduce a revised methodology and new tariffs midway through the current tariff period, which would result in a tariff increase of more than 50%. The TSO cites exceptional circumstances (a large drop in cross-system flows) as the reason for this change.
• Apply a uniform postage stamp reference price methodology with an ex-ante entry-exit split.
• Continue recovering transmission revenues through a mix of capacity-based charges (paid for reserving network capacity) and commodity-based charges (linked to the volume of gas transported).
• Adjust capacity tariffs at all entry and exit points (including domestic points) using benchmarking to lower tariffs and make them more competitive. Eustream proposes to use a wide set of European TSO tariffs, including those from Northwestern Europe, as a reference.
• Keep two commodity-based charges in place:
  • a flow-based charge paid in kind (meaning a portion of transported gas is normally used to cover the fee); and
  • a complementary revenue recovery charge, designed to help recover the costs of the Slovakia-Poland gas interconnector.

What are the key findings? 

ACER’s findings remain largely unchanged from its February 2026 report. After analysing the new consultation document, ACER concludes that: 

• The proposed methodology meets the EU requirement on non-discrimination.
• Compliance with the requirements on transparency, cost-reflectivity, avoidance of cross-subsidisation, volume risk and the prevention of cross-border trade distortions cannot be confirmed. This is mainly due to the proposed benchmarking adjustment, which does not meet the tariff network code’s standards.
• The proposed commodity-based charges are non-compliant. Specifically, the flow-based charge is corrected by a discount for domestic flows, which is not allowed under EU rules.

What does ACER recommend? 

Should the procedure be resumed, ACER recommends that ÚRSO:

• Limit benchmarking adjustments to points with clear pipeline competition, ensuring tariffs reflect market conditions and remain predictable for network users.
• Implement measures to improve alignment with the network code’s requirements, despite current challenges to full compliance.
• Phase out the non-compliant discount applied to the flow-based tariff.

See all ACER reports on national tariff consultation documents.