SHERIDAN, WYOMING - April 13, 2026 - The EU Agency for the Cooperation of Energy Regulators (ACER) has released its compliance assessment of Slovak gas transmission tariffs proposed by Eustream, Slovakia's transmission system operator, finding that key elements of the methodology fail to meet EU Network Code on Harmonised Transmission Tariff Structures (NC TAR) standards and issuing concrete corrective recommendations to the Slovak national regulator ÚRSO ahead of its final tariff decision.
What Eustream proposed
Eustream's proposed reference price methodology (RPM) covers the multi-year tariff period 2026-2027 and includes several substantive changes to current practice. The most consequential is a mid-period tariff revision that would increase charges by more than 70%, which Eustream justifies by citing exceptional circumstances - specifically, a large drop in cross-system gas flows that has materially reduced revenue recovery.
The methodology applies a uniform postage stamp approach with an ex-ante entry-exit split and retains a mix of capacity-based charges and commodity-based charges. Capacity charges apply at all entry and exit points, including domestic points, and are subject to a benchmarking adjustment using a wide set of European TSO tariffs - including those from Northwestern Europe - designed to lower tariffs and improve competitive positioning. Two commodity-based charges are kept in place: a flow-based charge paid in kind, where a portion of transported gas covers the fee, and a complementary revenue recovery charge designed to recoup costs associated with the Slovakia-Poland gas interconnector.
ACER's compliance findings
ACER confirmed that the proposed methodology meets the EU requirement on non-discrimination. However, compliance with several other NC TAR requirements cannot be confirmed, including transparency, cost-reflectivity, avoidance of cross-subsidisation, volume risk management, and prevention of cross-border trade distortions.
The primary driver of non-compliance is the benchmarking adjustment mechanism, which does not meet NC TAR standards because it is applied broadly rather than being limited to entry and exit points where pipeline-to-pipeline competition can be clearly identified. Additionally, the flow-based commodity charge is non-compliant because it applies a discount for domestic flows - a preferential treatment explicitly prohibited under EU rules. These two structural deficiencies undermine the tariff framework's predictability and cost-reflective integrity across the 2026-2027 period.
ACER's recommendations to ÚRSO
ACER directed three specific corrective actions at ÚRSO for incorporation into its final tariff decision. First, benchmarking adjustments must be restricted to entry and exit points where competition between pipelines is clearly identifiable, ensuring tariffs reflect actual market conditions and remain predictable for network users. Second, ÚRSO must implement measures to improve alignment with NC TAR requirements even where full compliance remains difficult given current operational challenges. Third, the non-compliant domestic flow discount applied to the flow-based tariff must be phased out.
These recommendations carry regulatory weight: ACER's assessments of national tariff consultation documents are formal inputs into national regulatory decisions, and persistent non-compliance with NC TAR exposes both the TSO and the national regulator to infringement proceedings at the EU level.
Business impact
Gas shippers and industrial off-takers routing volumes through Slovakia face direct exposure to a tariff increase exceeding 70% if Eustream's mid-period revision is adopted without modification. Procurement leads and energy trading desks must model revised transit cost scenarios for the 2026-2027 period now, since the final ÚRSO decision will set binding charges regardless of the benchmarking disputes ACER has flagged. Contracts indexed to Slovak transmission tariffs or structured around existing capacity reservations at domestic entry-exit points will require renegotiation or hedging adjustments.
For infrastructure and pipeline operators using the Slovakia-Poland interconnector, the continuation of a complementary revenue recovery charge linked to that corridor adds a layer of cost predictability risk. Operations directors and supply chain officers managing Central European gas routing must account for the possibility that ÚRSO adopts ACER's phased remediation approach - meaning tariff structures could shift incrementally across the 2026-2027 tariff period rather than being resolved at a single decision point. Regulatory affairs teams at affected shippers should engage ÚRSO's formal consultation process before the final decision to ensure their routing volumes are reflected in the competitive pipeline benchmarking analysis.