ACER Opinion 16-2026 on the reverse flow at the Murfeld/Ceršak cross-border interconnection point between Austria and Slovenia

No 16/2026

OPINION

on the coordinated decision concerning the prolongation of the exemption from the obligation to enable bi-directional capacity at the Murfeld/Ceršak cross-border interconnection point between Austria and Slovenia

11 September 2026

A C E R O P I N I O N N O 1 6 / 2 0 2 6

Executive summary

Under the European Security of Gas Supply Regulation, Transmission System Operators (‘TSOs’) are required to establish permanent physical capacity for gas transport in both directions (‘bi-directional capacity’) at all interconnection points between Member States. However, temporary exemptions may be granted following a detailed assessment and consultations with stakeholders, other Member States, and the European Commission. In this Opinion, ACER reviewed the coordinated Decisions adopted by the Austrian and Slovenian energy regulatory authorities, E-Control and AGEN-RS, acting as competent authorities for assessing the reverse flow procedures. The Decisions approve a joint proposal submitted by the Austrian and Slovenian TSOs, Gas Connect Austria and Plinovodi, respectively, to prolong until November 2029 the existing temporary exemption from the obligation to enable physical bi-directional capacity at the Murfeld/Ceršak interconnection point between Austria and Slovenia. ACER key findings are as follows:

1. the consultation and decision-making process was carried out by E-Control and AGEN-RS in a timely and coordinated manner.

2. the coordinated Decisions by E-Control and AGEN-RS comply with the legal requirements for the extension of an exemption from the obligation to enable permanent physical bi-directional capacity.

3. market signals do not indicate a need for bi-directional capacity from Slovenia to Austria at the Murfeld/Ceršak interconnection point; and

4. establishing such capacity in the absence of market demand would result in inefficient investments, as the costs would significantly outweigh the limited expected security-of-supply benefits for Austria. ACER, therefore, considers that the four-year prolongation of the exemption is justified, provided that no material changes occur in market conditions or infrastructure developments during this period. A C E R O P I N I O N N O 1 6 / 2 0 2 6

Table of contents

A C E R O P I N I O N N O 1 6 / 2 0 2 6

1. Background

1 Article 5(4) of Regulation (EU) 2017/1938 concerning measures to safeguard the security of gas supply (‘the SoS Regulation’) provides that transmission system operators (‘TSOs’) shall enable permanent physical capacity to transport gas in both directions (‘bi-directional capacity’) on all interconnections between Member States. The procedure for enabling bi-directional capacity or for granting an exemption from that obligation is laid down in Annex III to the SoS Regulation.

2 Under that procedure, the TSOs on both sides of the interconnection must submit to the competent authorities and regulatory authorities concerned a joint proposal for physical reverse flow capacity or a joint request for an exemption, including its possible prolongation.

3 Upon receipt of such proposal or request, the competent authorities concerned must consult, without delay, the authorities of any Member State that could benefit from the reverse flow capacity, as well as ACER and the European Commission (the Commission’). Those consulted may issue an opinion within four months.

4 The competent authorities concerned must adopt a coordinated decision, which may approve the proposal, grant or prolong a temporary exemption for up to four years, or require the TSOs to amend and resubmit their proposal or request. The coordinated decision is notified to the consulted authorities, the regulatory authorities concerned, ACER and the Commission, together with the opinions received. Within two months of that notification, the competent authorities consulted may raise objections.

5 Within three months of receipt of the coordinated decision, ACER must issue an opinion on its elements, considering any such objections, and submit that opinion to the competent authorities concerned, the consulted authorities and the Commission. Within four months of receipt of ACER’s opinion, the Commission may require modifications to the coordinated decision; if the Commission does not act within that period, it is deemed not to have raised objections.

6 An exemption from the bi-directional capacity requirement of the Murfeld/Ceršak interconnection point between Austria and Slovenia was first granted in 2012 under Article 7 of Regulation (EU) No 994/2010, then in force. Pursuant to point 13 of Annex III to the SoS Regulation, that exemption remained valid until the Commission requested to revise it in 2020. Following that review, the exemption was prolonged in 2022, in accordance with the procedure laid down in Annex III to the SoS Regulation, until November 2025.

7 In September 2025, before the expiry of the exemption, the Slovenian gas transmission system operator, Plinovodi, Družba za upravljanje s prenosnim sistemom, d.o.o. (‘Plinovodi’), and the Austrian gas transmission system operator, Gas Connect Austria GmbH (‘GCA’), jointly prepared a request to prolong the existing exemption for a further four years (‘Joint Proposal’). The Joint Proposal was submitted to the Austrian competent authority, Energie-Control Austria für die Regulierung der Elektrizitäts-, Gas- und Wasserstoffwirtschaft (‘E-Control’), and to the Slovenian competent authority, the Energy Agency of the Republic of Slovenia (‘AGEN-RS’) (together, the ‘Competent Authorities’) for a coordinated decision under Annex III to the SoS Regulation.

8 On 10 June 2026, E-Control and AGEN-RS adopted coordinated Decisions on that request prolonging for four years the existing exemption from the obligation to enable bi-directional capacity at the Murfeld/Ceršak interconnection point (the ‘coordinated Decisions’). ACER A C E R O P I N I O N N O 1 6 / 2 0 2 6 received AGEN-RS’s Decision No 112-15/2025/20 on 11 June 2026 and E-Control’s Decision No V REV G 01/25/3 on 12 June 2026. The coordinated Decisions are based on the Joint Opinion adopted by the Competent Authorities on 26 May 2026 and reach the same conclusion: to prolong the existing exemption for a period of four years, until November 2029.

9 This Opinion concerns the elements of those coordinated decisions. It is adopted pursuant to Article 9(4) of Regulation (EU) 2019/942, as well as Article 5(4) and point 8 of Annex III to the SoS Regulation and is addressed to the Commission and to all competent authorities concerned.

2. ACER assessment

10 In assessing the elements of the coordinated Decisions, ACER considered the requirements set out in Article 5 and Annex III to the SoS Regulation, the information submitted by E-Control and AGEN-RS, in particular the coordinated Decisions and the Joint Opinion, and the information submitted by Plinovodi and GCA, in particular the Joint Proposal to prolong the exemption. ACER received no objections pursuant to point 7 of Annex III to the SoS Regulation that would need to be taken into account for the purposes of the present assessment.

2.1. Assessment of the procedure

11 ACER notes that the Joint Proposal was prepared and consulted by the TSOs and the Competent Authorities in line with the requirements of Annex III to the SoS Regulation.

12 Under point 2 of Annex III to the SoS Regulation, the TSOs on both sides of the interconnection must submit the proposal or exemption request to the competent authorities and regulatory authorities concerned after consulting all transmission system operators potentially concerned. GCA and Plinovodi were of the view that the consultation with potentially concerned TSOs was not necessary, as the reverse flow at the Murfeld/Ceršak IP does not affect the security of supply of any other TSOs in the region. Following a request from E-Control and AGEN-RS, GCA and Plinovodi consulted the following TSOs between 1 and 15 December 2025: FGSZ, Bayernets, Natran, OGE, Net4Gas and Eustream. GCA received a response from FGSZ.

13 Under point 3 of Annex III to the SoS Regulation, upon receipt of a proposal or an exemption request, the competent authorities concerned must, without delay, consult the competent authorities and, where applicable, the national regulatory authorities of any Member State that could benefit from the reverse flow capacity, as well as ACER and the Commission. Those consulted may issue an opinion within four months of receipt of the consultation request.

14 Upon receipt of the Joint Proposal, E-Control and AGEN-RS jointly consulted the competent authorities of neighboring Member States with a natural gas transmission connection to Slovenia or Austria, namely Hungary, Croatia, Italy, Germany, Slovakia, Romania, as well as ACER, and the Commission. The consultation was open from 15 January to 15 May 2026. No responses were received.

2.2. Assessment of the elements of the coordinated Decisions

15 The coordinated Decisions approve the Joint Proposal of GCA and Plinovodi to prolong the exemption from the obligation of enabling bi-directional capacity at the Murfeld/Ceršak interconnection. They set out the relevant factual and legal background, describe the elements of the Joint Proposal, and explain the assessment of the Competent Authorities leading to those Decisions. In particular, the coordinated Decisions describe the cost-benefit analysis and the elements listed in Article 5(5) of the SoS Regulation, and assess the Joint Proposal against those requirements, and the conditions for prolonging an exemption set out in point 5(b) of Annex III. A C E R O P I N I O N N O 1 6 / 2 0 2 6

2.2.1. Conditions for prolonging the exemption

16 Under Article 5(5) and point 5(b) of Annex III to the SoS Regulation, an exemption from the obligation to enable bi-directional capacity may be granted or prolonged where the coordinated assessment shows, on the basis of the risk assessment, the required cost-benefit analysis and the consultation results, that enabling reverse flow would not enhance the security of gas supply of any relevant Member State, or that the investment costs would significantly outweigh the prospective security of gas supply benefits.

17 The Joint Proposal, and the coordinated Decisions approving the request, conclude that enabling bi-directional capacity at the interconnection point Murfeld/Ceršak pursuant to the SoS Regulation would not enhance the security of gas supply in Slovenia while it would improve the ‘N-1 criterion’ in Austria only marginally.

18 Both the TSOs and the Competent Authorities conclude that the investments costs needed in Austria and Slovenia for creating permanent bi-directional capacity at this interconnection point would significantly outweigh the prospective security-of-gas supply benefits. They also find that no interest in developing such capacity was expressed by market participants or by the consulted competent authorities concerned.

2.2.2. Costs and feasibility study of implementing bi-directional capacity

19 Based on the Joint Proposal, E-Control and AGEN-RS estimate that enabling a gas flow from 3 o Slovenia to Austria of 119 000 Nm /h (0 C) would require total investment costs of 64.4 EUR million, of which 38 EUR million would be incurred in Slovenia, and 26.4 EUR million in Austria. The annual operation and maintenance costs are estimated at 1.28 EUR million, of which 0.75 EUR million would be incurred in Slovenia, and 0.53 EUR million in Austria.

20 The Joint Proposal identifies the infrastructure upgrades required to enable bi-directional capacity. On the Slovenian side, this would require an upgrade of the Murfeld/Ceršak interconnection point and the second phase of the upgrade of the Kidricevo compressor station. On the Austrian side, it would require the outcrossing of the Weitendorf metering and transfer station, a new compressor station in Murfeld, and the outcrossing of the Murfeld metering and transfer station.

21 Those necessary investments could be implemented within 3.5 years on the Slovenian side and 4.5 years on the Austrian side, after the final investment decision would be taken.

22 ACER finds that the Joint Proposal contains sufficient information on the investments required to enable bi-directional capacity at the Murfeld/Ceršak interconnection point. In particular, the reverse-flow project proposal provides sufficient information on the basic design parameters of the main facilities, the proposed implementation schedule, the associated cost estimates and their margin of uncertainty.

2.2.3. Benefits to security of supply

23 According to E-Control, AGEN-RS, and the TSOs, enabling a minimum bi-directional flow at the Murfeld/Ceršak interconnection point from Slovenia to Austria would only have a negligible impact on Austria’s security of supply and on its compliance with the infrastructure standard. They note that the Austrian gas system currently exceeds the ‘N-1 criterion’ set out in Article 5 of A C E R O P I N I O N N O 1 6 / 2 0 2 6 the SoS Regulation by a wide margin, reaching 199%, compared with the required minimum threshold of 100%.

24 Furthermore, E-Control notes that the Austrian market is no longer primarily supplied via its historically dominant entry point, Baumgarten (i.e. Russian gas via Ukrainian route). In this market context, E-Control considers the N-1 indicator to be a potentially misleading measure for assessing system redundancy and security of supply in Austria. The main gas import route to Austria is now the Oberkappel entry point from Germany. However, even in the event of a disruption at Oberkappel, supply can be maintained through alternative import routes.

25 ACER takes note of this assessment and finds that establishing a bidirectional flow at the Murfeld/Ceršak interconnection point would only bring very limited security of supply benefits in Austria.

2.2.4. Cost-benefit analysis

26 The TSOs included a cost-benefit analysis, as required under Article 5(5) of the SoS Regulation. That analysis, while simplified, covers market demand, demand and supply projections, the potential economic impact on existing infrastructure, a feasibility study, and the costs of implementing bi-directional capacity, including the necessary reinforcement of the transmission systems. It concludes that the investment costs required to establish bi-directional capacity at the Murfeld/Ceršak interconnection point solely for security of supply purposes would significantly exceed the expected benefits for the Austrian gas system.

27 ACER considers the simplified methodology used by the TSOs and its conclusions reflected in the coordinated Decisions, to be reasonable. Although ACER notes that the cost-benefit analysis included in the Joint Proposal was not fully aligned with the ENTSOG methodology referred to in Article 11 of Regulation (EU) 2022/869 on guidelines for trans-European energy infrastructure (‘TEN-E Regulation’). ACER finds that the current TEN-E framework primarily applies to major new infrastructure projects (e.g. mostly large-scale electricity and hydrogen infrastructure) and is not well suited for reverse-flow projects, which are smaller in scale and different in nature.

2.2.5. Assessment of market demand, projections for demand and supply

28 Plinovodi and GCA identified no demand for permanent transmission capacity from Slovenia to Austria. Considering capacities available at other interconnection points, occasional use of interruptible reverse-flow capacity at the Murfeld/Ceršak interconnection point could be feasible through netting. In practice, however, this option has only been used sporadically and for very limited volumes.

29 Gas demand in Slovenia is expected to remain broadly stable, with only marginal increases foreseen. In Austria, gas consumption is projected to decline already by 2030 because of decarbonisation policies. Neither the national gas network plans nor the Union-wide Ten-Year Network Development Plan developed by ENTSOG foresee an increased need for gas flows from Slovenia to Austria.

30 ACER takes note of this assessment and has no observations.

2.2.6. Possible economic impact on existing infrastructure

31 The estimated investment costs of a reverse-flow project amount to EUR 38 million on the Slovenian side and EUR 26.4 million on the Austrian side. Such infrastructure would not be expected to operate under normal market conditions.

32 ACER notes that the costs of any reverse-flow projects would need to be recovered through tariffs, thereby creating upward pressure on transmission tariffs in both systems. A C E R O P I N I O N N O 1 6 / 2 0 2 6

2.2.7. Risk assessments

33 The findings of national risk assessments, as reflected in the latest available preventive action 6 7 plans for Austria and Slovenia , did not identify any positive effect of, or need for enabling bidirectional flow at the Murfeld/Ceršak interconnection point. Similarly, the most recent regional risk assessments for the Ukraine, Algeria, and Libya risk groups did not identify any security-ofsupply benefits associated with enabling such bi-directional capacity at that point.

34 ACER takes note of these assessments and has no observations.

3. Conclusions

35 ACER welcomes that GCA and Plinovodi worked together in preparing the Joint Proposal, and that the consultation and decision-making process was carried out by E-Control and AGEN-RS in a timely and coordinated manner in accordance with Annex III of the SoS Regulation.

36 ACER considers that the coordinated Decisions comply with the requirements of the SoS Regulation for the prolongation of an exemption from the obligation to enable permanent physical bi-directional capacity. In particular, the reasoning concerning the N-1 infrastructure standard is compelling, given that Austria already exceeds the required threshold by a wide margin and that the implementation of a reverse-flow project would only marginally improve that level in Austria.

37 ACER concurs with the conclusion that, both at the time of submission of the Joint Proposal and under the current conditions, market assessments do not indicate a need for bi-directional capacity from Slovenia to Austria at the Murfeld/Ceršak interconnection point. In those circumstances, establishing such capacity in the absence of market demand would lead to inefficient investments, as the costs, which would have to be included into the transmission tariffs, would significantly outweigh the limited expected security-of-supply benefits for Austria.

38 ACER, therefore, considers the proposed four-year prolongation of the exemption to be justified, provided that no material changes occur in market conditions or infrastructure developments during that period. This Opinion is addressed to the European Commission, all competent authorities concerned, and the competent authorities referred to in point 6 of Annex III to the SoS Regulation. Done at Ljubljana, on 11 September 2026. — SIGNED — V. ZULEGER, ACER Director ad interim