In its Summer Supply Outlook 2026, the European Network of Transmission System Operators for Gas (ENTSOG) evaluates the evolution of gas supply and assesses whether the EU’s gas system can meet demand, support exports and storage injections over the summer under normal market conditions.

The Outlook also includes an analysis of supplies and storage inventories to assess security of supply for winter 2026/27 and evaluates the system’s resilience under different stress scenarios, including supply disruptions.

ACER acknowledges the storage-filling challenges identified by ENTSOG. As this year’s reference scenario does not introduce major methodological changes compared with previous editions (extensively reviewed by ACER), ACER is not issuing a formal opinion on the 2026 edition.

What are the main highlights of the 2026 Summer Supply Outlook?

ENTSOG's assessment identifies several developments that will shape the EU’s gas system over the summer season:

• Low storage levels: At the start of the gas summer season (1 April 2026), average EU gas storage stood at 28% capacity, below the levels recorded at the start of the previous three summer seasons.
• High LNG demand: Refilling storage to the 90% target before winter (by 1 November) will require greater use of the EU’s gas infrastructure and higher liquefied natural gas (LNG) imports than in previous years. At the same time, ENTSOG notes that EU Gas Storage Regulation provides some flexibility, allowing a lower filling target.
• Supply disruption risks: The ongoing conflict in the Middle East is pushing up gas prices and narrowing the usual summer-to-winter price gap. This weakens the economic incentive for gas storage injections, which could further slow refilling.
• A resilient system: The EU’s LNG regasification capacity is expected to help compensate for lower storage levels and support winter demand, provided adequate LNG supplies are secured.

What are ACER’s main considerations?

ACER highlights the challenges ahead, as identified in ENTSOG’s assessment:

• The EU will need higher LNG imports. ACER’s latest analysis of European gas wholesale markets (winter 2025/2026) confirms that the EU’s LNG imports will need to rise by around 13% over 2025 levels to meet summer demand and reach the 90% filling target before winter, while the 80% target remains achievable with 2025 LNG import levels. This reflects LNG’s growing role in the EU’s energy mix: it covers around half of total gas imports, making the EU the world’s largest LNG importer (see also ACER’s analysis of European LNG market developments in 2025).
• Market conditions are weakening storage-filling incentives. Storage refilling could become more challenging in the months ahead. Unfavourable winter–summer price spreads, the phase-out of short-term Russian LNG and pipeline gas contracts under the REPowerEU Gas Regulation (from 25 April and 17 June 2026, respectively) and continued volatility due to the Middle East conflict constrain the supply available for storage, increasing the pressure to accelerate injections before November.
• Current data point to tight storage conditions:
  • Storage injections are below both the 10-year summer average and 2025 levels, putting the refilling timeline at risk (see Figure 1). 

  • EU gas storage is currently at around 49% capacity, similar to 2021 levels (see Figure 2).

Given these risks, ACER encourages Member States and their competent authorities to closely monitor storage-filling trajectories in the months ahead and foster continued progress, actively managing risks in compliance with the Gas Storage Regulation.

Looking ahead

ACER welcomes ENTSOG’s ongoing monitoring of storage injection trajectories and LNG import availability, as geopolitical instability continues to affect global energy markets.

For future Outlooks, ACER underlines the importance of continuing to assess how planned and unplanned gas supply disruptions may affect the EU’s ability to meet its storage-filling targets.

Finally, ACER highlights the need for timely storage injections in the coming months.

See all ACER’s reactions to ENTSOG’s Supply Outlooks.

The REPower Gas Regulation establishes an EU-wide ban on imports of pipeline gas and liquified natural gas (LNG) originating in Russia. It sets a timeline to phase out imports from Russia starting from March 2026 culminating in a full ban in November 2027. The Regulation mandates ACER to publish two monitoring reports (due on 1 July 2026 and 1 July 2027) which must provide:

• an overview of contracts for the supply of natural gas originating in, or exported directly or indirectly from, the Russian Federation to the European Union;
• data on natural gas originating in, or exported directly or indirectly from, the Russian Federation that transits through the EU;
• an assessment of the impact of supply diversification on EU energy markets.

What did ACER’s assessment find? 

• Long-term contracts for Russian gas remain in place in parts of the EU: Russian LNG contracts persist, with LNG cargoes landing in Spain, France, Belgium and the Netherlands. Currently, the total authorised contracts of Russian LNG held in Europe range from 20 to 32 bcm per year. Authorised pipeline gas contracts continue in Hungary, Slovakia and Greece. In total, EU pipeline gas annual contracts range from 16 to 26 bcm.
• Imported Russian gas is not necessarily consumed where it enters the EU: as gas may be traded and transported across borders, final consumption is difficult to trace.
• Russian gas still accounts for around 12% of EU gas demand. 
• Imports of Russian gas to the EU increased in early 2026, particularly: 
  • Between January and May 2026, pipeline imports rose 7% year-on-year while LNG imports increased by 11%.
  • Looking specifically at the time since the Regulation came into effect (18 March 2026), LNG imports increased by +17% from 18 March to 31 May 2026 (compared to the same period in 2025), despite a ban on short-term LNG imports since April 2026. Russian pipeline imports have increased by 5% year-on-year (18 March to end May). 
  • The increase in Russian LNG imports is driven by a combination of factors including frontloaded deliveries ahead of the tighter restrictions, contract adjustments, and some previously transhipped volumes which may have remained in the EU with the ban on transhipments. The current geopolitical context is also deemed relevant, pointing to efforts to maximise supply from alternative sources following the closure of the Strait of Hormuz. 
  • Limited early effects of the ban are visible, including lower pipeline flows via Türkiye Strandzha 1 (-65%, year-on-year from 18 March to end May 2026) after the ban kicked in on 18 March 2026. Stronger impacts are expected once the full LNG and pipeline bans take effect in 2027.

What’s next?

ACER will further assess the impact of the Russian gas phase-out in its 2027 report. It is currently too early to draw firm conclusions, as most phase-out measures have yet to be implemented in line with the regulatory calendar.  

The 2025 Consolidated Annual Activity Report outlines ACER’s regulatory work and achievements over the year. It also reviews how ACER delivered on its 2025 work programme. 

The report highlights ACER’s role in advancing the integration of the EU’s electricity and gas markets while safeguarding market integrity through surveillance activities under REMIT (the Regulation on Wholesale Energy Market Integrity and Transparency). 

It was adopted by ACER's Administrative Board on 28 May 2026, following approval by the Board of Regulators.

What were the main developments in 2025?

• Electricity markets: After several years of preparation, 2025 marked the launch of the 15-min market time unit for day-ahead and intra-day markets to better integrate renewable energy sources. Linked to this, ACER also worked to further foster demand response and flexibility, monitored related market barriers and the integration of additional transmission system operators (TSOs) into EU balancing platforms. During 2025, ACER also contributed to the investigation of major incidents, including the Iberian blackout. ACER also continued working on the implementation of the Network Code on Cybersecurity related to cross-border electricity flows.
• Gas and hydrogen markets: ACER took up new tasks under the recast Gas Regulation, focusing on the new provisions and advancing gas decarbonisation and the hydrogen market. This included developing a cost-efficiency comparison framework for natural gas TSOs and revising the Capacity Allocation Mechanisms and Interoperability Network Codes. ACER also continued to monitor wholesale gas and liquefied natural gas (LNG) markets and expanded its hydrogen market monitoring.
• Infrastructure & security of supply: ACER continued to assess EU infrastructure planning and possible improvements to the process, as set out in several opinions and reports. Other key monitoring reports identified best practices on transmission and distribution tariff methodologies. ACER also monitored security of supply within Europe and approved the European Resource Adequacy Assessment. A new workstream on flexibility was launched, with a first milestone reached in 2025 through ACER’s Decision on an EU-wide methodology to assess flexibility needs in Europe. 
• REMIT: ACER continued to improve and expand its market surveillance activities. In 2025, over 14,000 alerts were screened for potential market abuse and more than 1,300 cases shared with national regulatory authorities, leading to over €13 million in fines. ACER also collected more than 19 billion transaction records and published its first surveillance performance reports. It supported the implementation of revised REMIT and the European Commission’s preparation of the REMIT Implementing Regulation, as well as the Delegated Act for registered market participants and inside information platforms. ACER also launched the new REMIT Data Reference Centre and Inside Information Access Point.

In March 2026, ACER received a proposal from the European Network of Transmission System Operators for Electricity (ENTSO-E) to amend the methodology for the regional sizing of reserve capacity. After reviewing the proposal and exchanging with stakeholders, ACER has decided to amend the methodology.

What is the methodology about?

The methodology for the regional sizing of reserve capacity (first approved by ACER in 2023) allows regional coordination centres (RCCs) to assess the reserves needed at regional level, taking into account volumes shared between transmission system operators (TSOs) through bilateral agreements. 

This coordination helps reduce procurement costs and ensure a more efficient distribution of reserves across Europe. Based on their assessment, RCCs provide TSOs with recommendations on how to optimise reserve capacity volumes, leveraging the flexibility of the EU electricity system.

What’s new in the amended methodology?

As previously requested by ACER, the methodology now:

• Establishes that all RCCs must rely on data from the previous 12 months when assessing the minimum volume of reserves needed for the following year. This ensures the data used reflects the most relevant and frequent system conditions.
• Specifies, for each system operation region, how much reserve capacity is needed to cover positive and negative imbalances. 
• Introduces a 24-month rolling implementation deadline for assessing the short-term availability of reserve capacity (for sharing agreements established after 1 July 2026).
• Enhances transparency by strengthening and streamlining RCCs’ reporting obligations.

These changes will help RCCs size reserve capacity more efficiently, address TSOs’ operational risks and enhance the process’ transparency and coordination.

What are the next steps? 

As previously agreed, RCCs must implement the methodology’s main changes by 1 July 2026.