Short answer
EU competition law asks whether an undertaking has enough economic strength to act to an appreciable extent independently of competitors, customers and ultimately consumers, and thereby prevent effective competition from being maintained. Market share is important evidence, especially when it is very high and durable, but it is neither the whole test nor a substitute for defining the relevant market correctly.
The assessment therefore examines real competitive constraints. In a digital market, that may mean network effects, data, switching, multi-homing and distribution. In pharmaceuticals, therapeutic substitution, prescribing, reimbursement and patents may matter more than the patient's price. In network industries, control of infrastructure, legal exclusivity and access conditions may reveal power that sales shares miss.
No single factor automatically proves dominance. The evidence must show durable market power in the relevant product and geographic market during the period examined. Nor is dominance itself prohibited. Article 102 of the Treaty on the Functioning of the European Union (TFEU) prohibits its abuse, subject to the provision's territorial and trade conditions.
The legal test is independence, not size alone
prohibits abuse of dominance, not dominance itself. A business does not infringe it merely by gaining a leading position through competition on the merits.
Any abuse by one or more undertakings of a dominant position [...] shall be prohibited.
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The Court of Justice gave the enduring dominance test in United Brands, Case 27/76:
The dominant position referred to in this article relates to a position of economic strength enjoyed by an undertaking which enables it to prevent effective competition being maintained on the relevant market by giving it the power to behave to an appreciable extent independently of its competitors, customers and ultimately of its consumers. In general a dominant position derives from a combination of several factors which, taken separately, are not necessarily determinative. —
“Independently” does not mean completely free from every commercial constraint. It asks whether competitive reactions are strong and timely enough to discipline the undertaking's decisions. Evidence must therefore cover rivals, customers and entry, rather than only the undertaking's own size.
Market definition and shares remain the starting point
Dominance can be assessed only in a defined product and geographic market. A narrow market can inflate shares; an excessively broad one can conceal power. In innovative or regulated sectors, substitution may depend on functionality, clinical use, interoperability or access rather than price.
In AstraZeneca, Case C-457/10 P, the Court reiterated that a very large share held over time is, save in exceptional circumstances, proof of dominance, and described shares above 50% as very large. That evidence must relate to a soundly defined market and meaningful period.
Lower shares do not end the inquiry. In United Brands, a share above 40% and near 45% did not by itself establish automatic control. The Court examined the much smaller scale of competitors, vertical integration, secure supplies, logistics, brand strength, economies of scale, barriers to entry and the undertaking's ability to withstand competitive attacks. It also made clear that temporary losses were compatible with dominance. Profitability alone was not the test.
What replaces a simple price-and-share story?
The better question is: what could stop the undertaking from worsening terms, reducing quality, slowing innovation, excluding rivals or otherwise acting without effective discipline? The Commission's active enforcement-priorities guidance groups the core constraints as existing rivals, timely and sufficient entry, and buyer power. The evidence commonly falls into five groups:
- Entry and expansion: sunk costs, licences, access to infrastructure or inputs, time to scale, regulation and whether entry is likely, timely and sufficient.
- Customer responses: switching costs, contract duration, portability, multi-homing, buyer power and whether customers can sponsor entry or credibly move demand.
- Structural advantages: vertical integration, exclusive access, intellectual property, data, installed base, distribution, reputation and economies of scale or scope.
- Competitive performance: stability of position, rivals' failed expansion, the undertaking's response to entry, quality and innovation, not merely prices or accounting profits.
- Market design: zero-price services, reimbursement, regulated tariffs, network capacity or legal monopolies that make nominal prices a poor measure of constraint.
The same fact can point in different directions. Regulation may limit prices but protect incumbency. Intellectual property may reward innovation yet delay entry. Large buyers may constrain a supplier, unless switching is unrealistic.
Digital markets: users, data and feedback loops
Digital services may charge one user group nothing, so a price-based test can miss the competitive bargain. Authorities may need to examine several interdependent sides of a platform, including users, advertisers, merchants or developers. Relevant dimensions can include quality, privacy, attention, access to users and the ability to collect or use data.
The Google Shopping litigation provides a concrete example. The Commission found national markets for online general search and concluded that Google was dominant in 13 European Economic Area countries. As recorded by the Court of Justice in Case C-48/22 P, the evidence included high and stable usage shares, rivals' low shares, barriers to entry, limited use of more than one general search engine and Google's strong reputation. Google did not dispute the dominance finding before the General Court; the later appeal concerned the characterisation and effects of the conduct.
Data or network effects do not automatically prove dominance. The issue is whether they create an advantage rivals cannot realistically overcome. Actual switching, multi-homing, challenger innovation, interoperability and access to distribution can point the other way.
The Court's judgment of 2 July 2026 in Google Android, Case C-738/22 P, supplies a current warning against equating formal choice with effective constraint. It dismissed Google's appeal after recording that competing search or browser apps, although readily downloadable free of charge, were not downloaded in practice on enough devices to offset the pre-installation advantage. In a zero-price market, actual user behaviour and distribution defaults may therefore matter more than theoretical availability.
Pharmaceuticals: therapeutic and institutional constraints
Pharmaceutical prices can mislead because doctors choose treatments, third parties may reimburse them, and entry can depend on clinical evidence, marketing authorisation and patents.
In AstraZeneca, the Court upheld an assessment that looked beyond headline prices. It considered therapeutic efficacy, prescribing patterns, reimbursement, the limited price sensitivity of doctors and patients, first-mover status, brand reputation, financial strength and the practical use of patent rights. Higher prices combined with persistently much higher shares supported the conclusion that competitors, customers and consumers did not appreciably constrain the undertaking.
The Court nevertheless stressed that intellectual-property ownership alone does not confer dominance. The analysis is cumulative: patents, reimbursement and first-mover status may, with durable shares and weak substitution, explain why entry and customer reactions provide little discipline.
Energy and network industries: control can matter more than sales
In energy, rail, telecommunications and other network industries, the decisive asset may be infrastructure rather than the volume sold in a downstream market. Relevant evidence includes legal exclusivity, ownership or management of the network, spare capacity, connection and access rules, congestion, switching time and whether an alternative network is economically realistic.
The Lithuanian Railways appeal, Case C-42/21 P, illustrates this structure. The Commission identified an upstream Lithuanian market for railway-infrastructure management and a downstream market for rail transport of oil products. Lithuanian law entrusted the public railway infrastructure to the national railway company, giving it a legal monopoly upstream. The company was also, apart from very small quantities carried by a rival, the only undertaking active downstream. Those different facts supported dominance in the two markets.
Regulation may constrain tariffs while leaving control over access, capacity, timing or connections. Conversely, independent regulation, non-discriminatory access and credible alternative infrastructure may limit power. The assessment must test what the undertaking can actually do.
A practical evidence checklist
Before drawing a dominance conclusion, ask:
- What exact product and geographic market is being tested, and over what period?
- Are shares measured by revenue, volume, users, capacity, prescriptions, traffic or another metric that reflects competition?
- Are the shares durable, and how far behind are competitors?
- Can customers switch or use several suppliers without material cost, delay or quality loss?
- Can rivals enter or expand fast enough to discipline conduct?
- Does the undertaking control data, intellectual property, infrastructure, distribution or standards that rivals cannot replicate?
- Do regulation, reimbursement or legal exclusivity constrain power, reinforce it, or do both in different respects?
- What evidence could disprove dominance: rapid switching, successful entry, falling shares, buyer power or effective access remedies?
A list of advantages without evidence of durable independence is not enough.
Conclusion
EU law establishes dominance by assessing durable economic independence in a properly defined market. Very high, stable shares can be decisive, but complex markets demand evidence about the constraints behind them. Digital feedback loops, therapeutic substitution, network control, entry, switching and buyer power can reveal—or rebut—market power that price and shares would misstate.
The legal test remains the same across sectors. What changes is the evidence needed to show whether competitors, customers and consumers can effectively discipline the undertaking during the relevant period.
Sources
This article provides general legal information, not advice for a specific matter. Laws, facts and procedural deadlines may change the result. Follow the linked primary sources and obtain local advice before acting.