The Role of Concentration and Collusion in Oligopolistic Markets

Walk into any telecom store in India and you will notice something odd. Jio, Airtel, and Vi tend to revise their tariffs around the same time, often by similar margins. This is not a coincidence. It is a textbook feature of an oligopoly, a market structure where a small number of large firms dominate supply and watch each other’s every move. When these firms stop competing and start coordinating, the market shifts from rivalry to collusion, and understanding this shift is central to studying how concentrated industries actually behave.

What makes a market oligopolistic 🔗

An oligopoly exists when a handful of firms account for most of an industry’s output. Because there are so few players, each firm’s pricing or output decision directly affects its rivals, unlike in perfect competition where individual firms are too small to matter. This mutual dependence is what economists call strategic interdependence, and it is the seed from which collusion grows.

Measuring concentration 🔗

Economists rarely rely on guesswork to decide whether a market is concentrated. Two tools are commonly used. The concentration ratio simply adds up the market shares of the top firms, usually the top four (CR4). The Herfindahl-Hirschman Index (HHI) goes further by squaring the market share of every firm in the industry and summing the results, which gives more weight to genuinely dominant players.

A high HHI signals that a market is structurally suited to collusion, because fewer, larger players find it easier to reach an understanding than dozens of small, scattered competitors would.

Why oligopolists choose to collude 🔗

Left to pure rivalry, oligopolists face a strange paradox. If every firm keeps cutting prices or expanding output to grab market share, industry profits fall for everyone, even though each firm is behaving rationally on its own. Collusion offers an escape route. By agreeing, formally or informally, on prices, output, or market territory, firms can behave collectively like a single monopolist and capture higher joint profits than competition would ever allow them individually. Reduced uncertainty is an added benefit. Firms no longer need to guess how rivals will react to a price cut, because the rules of engagement are already settled between them.

Formal collusion: cartels and explicit agreements 🔗

Formal collusion happens through an explicit understanding among firms, an arrangement historically called a cartel. Cartel members openly agree on prices, production quotas, or market shares, often through a coordinating association or committee. Global cartels are rare and usually illegal, though there are famous exceptions. OPEC, the group of oil-exporting nations, is the textbook example of a cartel that meets regularly to agree on production targets in order to influence global oil prices.

How a cartel sets its price and output 🔗

Cartel behaviour follows the same logic as a monopolist’s, just applied jointly. The outline for this unit points to a specific tool: the aggregate marginal revenue and marginal cost curves. Here is how it works. The cartel first estimates the market’s overall demand curve and derives its corresponding marginal revenue (MR) curve. On the cost side, it adds up the marginal cost curves of every member firm to get an aggregate marginal cost curve, generally written as ΣMC. Joint profits are maximised at the output where this aggregate marginal cost curve intersects the market marginal revenue curve, exactly where a single monopolist would set output.

Once that total industry output is fixed, the cartel allocates production among member firms so that each firm’s individual marginal cost equals the common industry marginal revenue. This ensures the cheapest possible production of the agreed total. Firms with lower costs end up producing more, and higher-cost firms produce less, even though every member shares in the resulting monopoly-style profit through pre-agreed quotas or side payments.

Informal collusion: coordination without a contract 🔗

Not every instance of coordinated behaviour involves a signed agreement. Tacit collusion occurs when firms arrive at similar pricing or output decisions through repeated observation of each other’s behaviour, without ever discussing it directly. No contracts, no meetings, sometimes not even a phone call. Firms simply learn what rivals will tolerate and adjust accordingly.

Price leadership as an informal mechanism 🔗

The most common form of tacit collusion is price leadership. A dominant or lowest-cost firm sets its price, and the rest of the industry falls in line without any explicit coordination. This is common in industries with a clear market leader and creates the appearance of price uniformity that looks almost identical to formal cartel pricing, but is far harder for regulators to prove, since liability in most cartel cases still depends on establishing some form of proven awareness or communication between the parties.

The consumer cost of concentrated power 🔗

Whether collusion is formal or tacit, its consequences for consumers are similar. Colluding firms restrict total output below competitive levels and push prices above what a genuinely competitive market would produce, which is precisely the monopoly-style outcome the aggregate MR-MC framework predicts. Consumers pay more for less choice, innovation incentives weaken since firms no longer need to compete aggressively to retain customers, and smaller potential entrants find it harder to break into a market where incumbents are effectively acting as one unit.

India has seen this play out in concrete cases. Cartel behaviour tends to concentrate industry profits among a handful of firms while the wider economy loses out on the efficiency gains that competition usually delivers.

How India regulates collusion and concentration 🔗

Cartel conduct is governed in India under the Competition Act, 2002, enforced by the Competition Commission of India (CCI). Section 3 of the Act treats agreements among competitors that fix prices, limit production, or share markets as presumptively harmful to competition. One of the CCI’s largest enforcement actions came in 2016, when it penalised eleven cement manufacturers over ₹6,300 crore for using their trade association to restrict supply and fix prices, a case that began with a complaint from the Builders’ Association of India.

Regulators do not always need proof of a formal agreement to act. In cases involving digital marketplaces, the CCI has examined whether large platforms exercise what is called collective dominance, where two or three dominant firms in an oligopoly can coordinate behaviour through sheer interdependence, even without a written pact. To encourage cartel members to come forward voluntarily, the CCI also runs a leniency programme that offers reduced penalties to firms or individuals who disclose evidence of a cartel’s existence before the regulator completes its own investigation.

Why collusive arrangements often break down 🔗

Cartels carry a built-in tension. Every member has a private incentive to secretly undercut the agreed price or exceed its output quota, since doing so captures extra sales at the cartel’s expense while the higher price umbrella still holds for everyone else. If enough members give in to this temptation, the entire arrangement unravels, prices fall, and the industry reverts toward more competitive behaviour, at least until a fresh attempt at coordination emerges. This instability is one reason why sustained cartels are relatively rare without either a strong internal enforcement mechanism, such as a dominant lead firm punishing deviators, or a trade association making prices and sales data visible enough for members to detect cheating quickly.

What does this mean for how you read industry pricing 🔗

Concentration and collusion are two sides of the same coin. Few firms create the conditions for coordination, and coordination, once it takes hold, deepens the market’s effective concentration by making the industry behave as if it were a single decision-maker. Recognising the signs, near-identical price movements, unusually stable margins across firms, or a dominant player everyone else quietly follows, is a useful skill whether you are studying microeconomics, evaluating an investment, or simply trying to understand why your monthly phone bill rarely goes down even when new technology should be lowering costs.

What do you think? The next time you notice two or three brands in the same industry raising prices within days of each other, would you read that as coincidence, tacit collusion, or simple price leadership? And should regulators like the CCI have the power to act against coordinated behaviour even when no explicit agreement can be proven?

References

1. https://www.justice.gov/atr/herfindahl-hirschman-index
2. https://www.economicsdiscussion.net/oligopoly/cartels-types-joint-profit-maximisation-and-market-sharing-cartel/7370
3. https://blog.primelegal.in/cci-ai-cartels-competition-act-guide/
4. https://www.mondaq.com/india/cartels-monopolies/936392/competition-commission-in-india-and-regulations-governing-cartels-
5. https://indiacorplaw.in/2022/01/05/oligopoly-competition-cartels-and-beyond-establishing-the-need-for-collective-dominance/