Introduction

On 9 September 2026,¹ the General Court of the European Union (“General Court”) dismissed a challenge by Booking Holdings Inc. (“Booking”) against the blocking by the European Commission (“Commission”) of Booking’s proposed acquisition of eTraveli Group AB (“Etraveli”). In doing so, the General Court upheld one of the Commission’s most closely watched and debated merger decisions in recent years.

The judgment is noteworthy well beyond the online travel sector. For the first time, the EU courts have endorsed a “reverse leveraging” theory of harm in a conglomerate merger: a transaction may significantly impede effective competition where an undertaking may be capable of leveraging an activity in a market in which it is not dominant, to reinforce an existing dominant position in a neighbouring market. In doing so, the Court made clear that what matters is the resulting reinforcement of that dominant position, including through higher barriers to entry or further entrenchment, rather than the direction of the leveraging or the magnitude of any increase in market share.

Perhaps even more significantly, the General Court confirmed that the Commission does not necessarily need to demonstrate that a transaction will result in a substantial quantitative increase in market power: even an increment of a fraction of a percentage point could be sufficient where the transaction reinforces network effects, raises barriers to entry and expansion and, more broadly, consolidates and perpetuates an already low level of competition.

The judgment therefore provides important guidance for transactions involving dominant companies acquiring complementary businesses, particularly in digital and ecosystem-driven markets.

Background

Booking is principally active as a hotel online travel agency (“OTA”), while Etraveli operates primarily as a flight OTA. Although the parties overlapped to some extent in flight OTA services, their relationship was primarily complementary.

The Commission nevertheless prohibited the transaction in September 2023.² It found Booking to be dominant in the EEA-wide hotel OTA market and considered that acquiring Etraveli would give Booking control over an important customer-acquisition channel—flights—which it could use to attract additional hotel customers. The Commission’s decision contrasted with its UK counterpart’s, which cleared the same transaction in Phase I finding that Etraveli was not a particularly significant customer retention and/or acquisition channel for hotel OTAs in the UK.³

The Commission's theory was essentially that acquiring Etraveli would enable Booking to accelerate the growth of its flight offering and use the resulting customer traffic and data to cross-sell hotel accommodation. This would reinforce the network effects already protecting Booking's hotel OTA position, increase barriers to entry and expansion for rival OTAs and ultimately make Booking's dominant position less contestable.

Booking challenged the prohibition before the General Court, arguing, among other things, that the Commission had departed from its Non-Horizontal Merger Guidelines (“Guidelines”), relied on an unprecedented theory of ‘reverse leveraging’, used an incorrect counterfactual, and failed to establish a significant impediment to effective competition (“SIEC”) to the requisite legal standard.

‘Reverse leveraging’ becomes an established theory of harm

One of the most important aspects of the judgment is the General Court's endorsement of the Commission's ‘reverse leveraging’ theory.

Conglomerate mergers, as acknowledged by the General Court in Tetra Laval B.V. v Commission, were traditionally seen as generally neutral or even beneficial to competition and therefore “proof of anti-competitive conglomerate effects of such a merger calls for a precise examination, supported by convincing evidence, of the circumstances which allegedly produce those effects” (Cases T-5/02 and T-80/02, para. 155).

Additionally, conglomerate leveraging concerns have historically focused on the use of market power in one market to strengthen a position in another: the Commission’s Guidelines (2008) at footnote 84 explain that, while there is no generally accepted definition, in a neutral sense leveraging “implies being able to increase sales of a product in one market (the ‘tied market’ or ‘bundled market’), by virtue of the strong market position of the product to which it is tied or bundled (the ‘tying market’ or ‘leveraging market’)”. Booking argued that the Commission's approach effectively reversed that logic: Booking was not dominant in flight OTA services, but would use Etraveli's position in flights to reinforce its existing dominance in hotel OTA services.

The General Court rejected this distinction.

It held that leveraging is a generic concept describing the impact that conduct or a position on one market may have on another. From a competition perspective, the potential effect is essentially the same irrespective of the direction in which the leverage operates. It would therefore be contradictory to permit intervention where leverage strengthens a non-dominant position but to prevent it where the same mechanism strengthens an already dominant position.

In the General Court's view, such a restriction would risk undermining the effectiveness of EU merger control.

Importantly, the General Court also rejected the suggestion that the Commission had unlawfully departed from its Guidelines (those Guidelines provide a general analytical framework rather than an exhaustive catalogue of permissible theories of harm). In particular, the General Court recognised that digital markets may generate competition concerns that were not fully anticipated when the Guidelines were adopted in 2008.

For dominant businesses considering acquisitions of complementary assets, this significantly broadens the range of conglomerate transactions that may require careful competition law assessment.

A small increment can still produce a significant impediment to competition

The judgment's second major contribution concerns the relationship between market-share increments and the SIEC test.

The General Court accepted that the transaction-specific increment in Booking's market share in flight OTA services could potentially amount to only a few tenths of a percentage point, insofar as this could translate into growth in its hotel OTA business as a result of cross-sales of hotel rooms from flights.

The General Court emphasised that there is no automatic equivalence between dominance and a SIEC. A transaction involving an already-dominant undertaking must still result in a SIEC within the meaning of Article 2(3) of the EU Merger Regulation.

However, in order for an anticompetitive effect to be treated as “significant” in this context, a large, measurable deterioration in competitive conditions following the transaction is not necessarily required. A merger may also significantly impede competition by consolidating and perpetuating an already low level of competition.

That distinction is particularly important in markets characterised by strong network effects. A relatively small increase in the customer base of an already dominant platform may strengthen those network effects while simultaneously limiting rivals' ability to expand. The competitive significance of the transaction may therefore be substantially greater than the corresponding percentage-point increase in market share suggests.

In Booking/Etraveli, that concern was reinforced because, in the Commission’s (and General Court’s) view, the transaction would give Booking greater access to one of the few customer-acquisition channels that it did not already dominate (flights) and facilitate the creation of a broader travel ecosystem that rivals would find difficult to replicate.

Qualitative evidence matters as much as the numbers

The judgment also provides an important reminder that merger assessment cannot be reduced to market-share calculations or quantitative modelling.

Booking sought to distinguish between the Commission's quantitative evidence, including its estimates of the market-share increment and qualitative considerations relating to network effects, customer acquisition, data and ecosystem advantages.

The General Court rejected such a rigid distinction. Quantitative and qualitative evidence will frequently overlap, and the Commission is entitled to base its assessment on qualitative factors provided that the overall body of evidence is sufficiently cogent and consistent and capable of supporting the conclusions drawn from it.

This proved decisive in the case. Booking succeeded in demonstrating a number of shortcomings in the Commission's quantitative analysis; however, those errors did not undermine the core mechanism underlying the theory of harm.

The practical message is important: successfully challenging individual calculations will not necessarily undermine a prohibition decision where the broader competitive narrative remains intact. Parties challenging a novel theory of harm will therefore need to focus on the structural and economic mechanism underpinning the Commission's case, rather than the arithmetic alone. This is particularly salient as the forthcoming Merger Guidelines are expected to give greater prominence to novel and developing theories of harm.

Efficiencies must be properly presented and substantiated

The judgment is equally instructive on efficiencies.

Before the General Court, Booking relied on several alleged benefits of the transaction, including the convenience and consumer benefits associated with creating a “one-stop shop” for flights and accommodation.

However, from a procedural perspective, as the General Court emphasised, those arguments must be properly presented as efficiencies during the administrative procedure. General references to consumer benefits in the EU merger control notification form (i.e., Form CO or other submissions) are not necessarily sufficient. The General Court therefore rejected Booking's one-stop shop argument where the claimed benefit had not expressly been advanced as an efficiency during the Commission's investigation.

For merging parties, this reinforces the importance of identifying, substantiating and wherever possible quantifying efficiencies early on in the merger review process rather than treating them as afterthoughts that can be developed once competition concerns have crystallised.

Practical implications

The judgment stands to give the Commission considerable latitude in assessing acquisitions by dominant companies, particularly where complementary products, customer-acquisition channels, data and network effects interact.

This raises three matters in particular that could have implications for future merger enforcement in the EU.

First, conglomerate transactions involving dominant firms may end up being subject to increased scrutiny for reverse leveraging. The absence of dominance or even substantial market power in the target's market does not exclude concerns where the acquired activity can reinforce dominance elsewhere.

Second, market-share increments may become less informative as a standalone measure of merger risk in highly concentrated or network-driven markets. Where competition is already weak, the Commission may focus on whether a transaction makes the incumbent's position less contestable by strengthening network effects, expanding its ecosystem or depriving rivals of opportunities to scale up.

Third, the judgment underlines the importance of developing transaction parties' affirmative case early on, supported, ideally, by internal documents, to shape the Commission’s understanding of the case from the outset.

Looking ahead

The judgment in Booking Holdings v Commission represents an important judicial endorsement of the Commission's increasingly effects-based and forward-looking approach to non-horizontal mergers.

The judgment does not establish that every strengthening of a dominant position, however marginal, constitutes a SIEC; indeed, the General Court expressly maintains the distinction between dominance and the SIEC test. Its significance lies instead in confirming that, in an already concentrated market characterised by strong network effects and limited contestability, the competitive significance of a transaction may substantially exceed its measurable market-share increment.

The judgment is also particularly timely given the Commission's ongoing revision of its Merger Guidelines. Concepts such as ecosystems, entrenchment, network effects and broader dynamic competitive effects already feature prominently in the Commission's proposed framework. Booking Holdings v Commission may encourage the Commission to consider that it has judicial support to look beyond conventional horizontal overlaps and short-term market-share effects, to examine whether an acquisition reinforces the structural advantages protecting an incumbent's position.

For companies with strong market positions, acquisitions of complementary businesses, customer-acquisition channels or data-rich assets may therefore warrant substantive merger-control analysis well before traditional market-share screens would suggest a concern. The judgment may not, however, be the final word: Booking has indicated that it disagrees with the outcome and is considering an appeal to the Court of Justice, which may be brought on points of law by late November 2026.

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¹ Booking Holdings v Commission, Case T-1139/23.
² Commission Decision of 25 September 2023 - Case M.10615, Booking Holdings/Etraveli Group.
³ UK Competition & Markets Authority, Anticipated acquisition by Booking Holdings Inc. of certain activities of eTraveli Group AB, Case ME/6991/22, 29 September 2022, para. 9.

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