Short answer
There is no special evidentiary test for an “algorithmic cartel”. Under Article 101 TFEU, the authority or claimant must prove an agreement, a decision by an association of undertakings, or a concerted practice, together with the required effect on trade and restrictive object or effect. Direct evidence of a formal deal is unnecessary. A firm, precise and consistent body of objective indicia can establish coordination.
What matters is whether competitors knowingly replaced competitive uncertainty with practical cooperation. Relevant evidence may include instructions encoded in a shared pricing tool, commercially sensitive inputs channelled through a platform or trade association, messages showing awareness, acceptance of a common pricing rule, reactions to rivals' signals, and subsequent market conduct. Once participation in concertation and continued market activity are shown, EU law permits a rebuttable presumption that the information influenced conduct.
Matching prices, similar software, association membership, or genuinely public current-price announcements do not alone prove collusion. Parallel conduct must be tested against plausible independent explanations and the full legal and economic context.
The legal test is technology-neutral
expressly covers three forms of coordination.
“The following shall be prohibited as incompatible with the internal market: all agreements between undertakings, decisions by associations of undertakings and concerted practices which may affect trade between Member States and which have as their object or effect the prevention, restriction or distortion of competition within the internal market, and in particular those which:”
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An agreement need not be signed. A trade association's rule may itself be a decision by an association of undertakings. A concerted practice catches coordination that has not reached a formal agreement but knowingly substitutes practical cooperation for competitive risk. It generally requires concertation, later market conduct and a causal connection between them.
Article 2 of places the burden of proving an Article 101(1) infringement on the party or authority alleging it. In national proceedings, domestic rules govern evidence and the standard of proof, subject to EU principles of equivalence and effectiveness and the presumption of innocence.
That framework permits circumstantial proof. In , the Court held that objective and consistent indicia can establish an infringement. One ambiguous data point or a technical capability is not enough.
What must be shown when an algorithm is involved?
The first question is what the software actually does. A firm may independently use an algorithm to observe genuinely public prices and set its own price. Similar outputs can arise from similar inputs and market conditions without contact between competitors. By contrast, a shared tool may receive non-public future prices, apply a common pricing instruction, transmit one competitor's intentions to others, or monitor compliance with an existing cartel.
The Commission's non-binding explain that information can pass indirectly through a platform, algorithm or trade association. They distinguish use of public data from aggregating competitors' sensitive information in a shared pricing tool. A shared rule to price relative to a competitor can be caught without an express promise.
For each participant, evidence should address knowledge and contribution. Did the firm supply sensitive inputs knowing they would reach rivals? Did it expressly or tacitly accept the shared rule? Could it reasonably foresee onward disclosure and accept that risk? Did it receive a competitor's plans and act on them? In , the Court held that conduct by an independent service provider can be attributed where the provider acted under the firm's direction or control, the firm knowingly intended to contribute to the anti-competitive objective, or it reasonably foresaw the conduct and accepted the risk.
A technology provider can also incur liability. confirms that Article 101 is not limited to firms in the cartelised market. A consultant that knowingly organised meetings, supplied data and monitored the cartel participated; neutral software supply is different.
A current platform example is the Commission's June 2025 . The parties acknowledged a no-poach arrangement, exchanges of commercially sensitive information and market sharing. The evidence included emails, WhatsApp messages, calls, meetings and internal reporting. Exchanged subjects included pricing, capacity, delivery zones and dispatching algorithms.
A message or shared restriction is evidence, not automatic guilt
Eturas concerned travel agencies using a common online booking system. The administrator sent a system message about a discount cap and introduced a technical restriction. The Court rejected automatic liability merely because the message was dispatched.
“The presumption of innocence precludes the referring court from inferring from the mere dispatch of the message at issue in the main proceedings that the travel agencies concerned ought to have been aware of the content of that message.”
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Other objective and consistent indicia could nevertheless support a rebuttable inference of awareness. Once awareness was established, tacit assent plus the other elements of a concerted practice could be found. A participant could rebut the inference by proving non-receipt, a clear objection, reporting the conduct, or systematic pricing above the imposed discount cap.
Logs showing delivery, access and use matter, alongside permissions, configuration changes, internal discussions, overrides and timing. Silence is probative when the recipient understood the proposal and remained active; it is not a substitute for awareness.
What changes when communication runs through a trade association?
An association can be a legitimate collector of aggregated, historical market information. The 2023 Horizontal Guidelines state that sufficiently aggregated information is generally less likely to restrict competition, although even aggregation can facilitate collusion in a tight, stable oligopoly.
Risk increases where an association circulates identifiable, recent or future prices, output, capacity, customers, costs or strategy; convenes discussions about members' intended responses; recommends a coordinated parameter; or helps detect deviations. Minutes, agendas, presentations, data-submission rules, distribution lists, individualised reports and messages before and after meetings can together prove the channel and participants' knowledge.
Membership alone does not prove participation. Evidence should identify who supplied or received information, what each participant knew, any distancing, and the relationship to later conduct. A recommendation may instead qualify directly as an association decision.
When do public pricing signals cross the line?
Public visibility neither legalises nor condemns a statement. A current retail price normally supports customer comparison. A specific, non-binding future intention may give rivals a focal point, especially when they respond and revise announcements after observing one another.
The limiting principle comes from the 1993 .
“Parallel conduct cannot be regarded as furnishing proof of concertation unless concertation constitutes the only plausible explanation for such conduct.”
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There, quarterly customer announcements were rational in a transparent, long-term market, and the Commission lacked firm, precise and consistent evidence of prior concertation. By contrast, in the Commission's , carriers repeatedly announced revisable future increases weeks ahead and rivals often followed. The Commission accepted commitments; the Article 9 decision was not a final infringement finding.
Strong public-signal evidence combines future sensitive detail, limited customer value, concentrated and transparent conditions, reciprocal reactions, private contacts or internal records describing an invitation to coordinate.
An evidence checklist
Ask whether the file establishes:
- the precise communication, common rule or association decision;
- commercially sensitive content, especially future prices, quantities, capacity or customers;
- each participant's awareness, contribution, foreseeability or control;
- later conduct, timing and the required causal link;
- market conditions and credible independent explanations;
- distancing, reporting, overrides or other rebuttal evidence; and
- restrictive object or effect and an effect on Member State trade.
In , one meeting could suffice to coordinate a competitive parameter. Once concertation and continued activity are proved, participants are presumed, subject to rebuttal, to have used the information. Contact and participation must still be proved first.
Conclusion
Algorithms, associations and public statements can carry coordination without a written cartel agreement. Proof must still show knowing contact or a common decision, participation and the required connection to conduct. Technical similarity or price parallelism remains insufficient where independent behaviour is plausible.
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.