Different market structures

Both a perfectly competitive firm and a monopoly maximise profit where MC = MR, but their market conditions produce very different long-run equilibria.

Perfect competition. With very many firms, an identical product, free entry and perfect information, each firm is a price-taker: its demand curve is horizontal, so AR = MR = price. In the short run a firm can earn supernormal profit (if price > ATC) or losses. But because entry is free, supernormal profit attracts new firms, raising market supply and lowering the price until price = ATC; losses cause exit until normal profit is restored. So in long-run equilibrium the firm earns only normal profit (P = AR = ATC), producing where P = MC = ATC (minimum). This makes perfect competition allocatively efficient (P = MC) and productively efficient (minimum ATC).

Monopoly. A monopoly is a single firm protected by high barriers to entry, so it is a price-maker facing the downward-sloping market demand curve, with MR < AR. It maximises profit where MC = MR, then charges the higher price on the demand curve, producing a lower output and higher price than perfect competition. Because barriers prevent entry, it can sustain supernormal profit in the long run. Since P > MC, it is allocatively inefficient (under-production, deadweight loss), and it may be productively inefficient (not at minimum ATC) and X-inefficient.

Key differences. In long-run equilibrium, the competitive firm earns only normal profit and is efficient (P = MC, min ATC), whereas the monopoly earns supernormal profit and is inefficient (P > MC), with higher prices and lower output. The crucial reason is barriers to entry: free entry competes away the competitive firm's profit, while barriers protect the monopolist's. (However, the monopoly may achieve economies of scale and dynamic efficiency through R&D, which can partly offset its static inefficiency.)

A monopoly is a single dominant firm protected by high barriers to entry. The view that it is always against consumers' interests has strong support but important exceptions.

The case that monopoly harms consumers. A monopoly is a price-maker that maximises profit where MC = MR, setting a higher price and lower output than a competitive market. Because P > MC, it is allocatively inefficient, causing under-production and a deadweight welfare loss — consumers value extra units more than they cost, but the monopoly restricts supply to raise price. It can sustain supernormal profit in the long run (barriers prevent entry competing it away), redistributing surplus from consumers to the firm. Without competitive pressure, a monopoly may also become X-inefficient (complacent, high costs) and offer less choice and poorer service. On these grounds, monopoly clearly harms consumers.

The case that monopoly can benefit consumers. First, a large monopoly may enjoy substantial economies of scale, giving it lower long-run average costs than many small firms — and if some savings are passed on, prices could be lower than under fragmented competition. This is especially true of a natural monopoly (e.g. water, rail track), where competition would wastefully duplicate infrastructure. Second, the supernormal profits can fund research and development, raising dynamic efficiency — new and better products over time, which benefits consumers. Third, monopolies may exploit their scale to compete internationally. Fourth, where the market is contestable (low barriers to entry/exit), even a monopolist behaves competitively to deter entry, keeping prices low.

Judgement. Monopoly is often, but not always, against consumers' interests. In the standard case — high barriers, no contestability, no efficiency gains — it is statically inefficient and exploitative, clearly harming consumers. But where it achieves significant economies of scale (especially a natural monopoly), drives innovation (dynamic efficiency), or operates in a contestable market, it can benefit consumers through lower costs/prices and better products. The most defensible conclusion is that whether monopoly harms consumers depends on the specific circumstances — economies of scale, dynamic efficiency, and contestability. This is why governments typically regulate monopolies (e.g. price caps, promoting competition) rather than banning them outright: to capture the scale/innovation benefits while limiting the exploitation. So 'always against consumers' is too strong.

5-firm concentration ratio = sum of the five largest firms' market shares = 22 + 18 + 14 + 11 + 9 = 74%.

This means the top five firms control 74% of the market, which is fairly highly concentrated — consistent with an oligopoly, where a few large firms dominate.

This suggests the firms are likely to be interdependent: each will consider rivals' reactions when setting prices, so we might expect non-price competition (branding, advertising), some price rigidity, and the possibility of collusion to raise prices toward the monopoly level.

However, the concentration ratio alone is not conclusive about how competitively the firms behave. The market could still be contestable — if barriers to entry and exit are low (no significant sunk costs), the threat of new entrants would keep prices and profits down despite the high concentration. Conversely, high barriers would allow the dominant firms to exploit their market power. So while the 74% ratio indicates an oligopolistic structure, the actual outcome for consumers depends also on contestability and barriers to entry, not just the number of firms.

An oligopoly is dominated by a few large interdependent firms, where each firm's actions depend on rivals' likely reactions. This interdependence helps explain a preference for non-price competition (branding, advertising, quality, loyalty schemes) over price competition.

Why price competition is risky. Because firms are interdependent, a price cut by one firm is likely to be matched by rivals (to avoid losing market share). If all firms cut prices, none gains much market share but all earn lower revenue and profit — a mutually damaging price war. The kinked demand curve model captures this: rivals follow price cuts (so demand is inelastic below the current price, and a cut gains little) but ignore price rises (so demand is elastic above it, and a rise loses customers), making firms reluctant to change price — hence price rigidity. The Prisoner's Dilemma reinforces this: competing on price leaves both firms worse off than cooperating.

Why non-price competition is attractive. Non-price methods — advertising, branding, product quality, customer service, loyalty schemes — can increase a firm's market share and brand loyalty without triggering a price war. They make demand more inelastic (loyal customers are less price-sensitive), allowing the firm to protect or raise profit. They are also harder for rivals to copy quickly than a price cut, so the advantage can last longer. Large oligopolists have the supernormal profits to fund expensive advertising and R&D.

Judgement. Firms in an oligopoly tend to prefer non-price competition because price competition is mutually destructive (matched cuts, price wars) while non-price competition can build market share and loyalty without provoking retaliation, and can make demand less elastic. However, this is not absolute: price competition does occur (e.g. supermarket price wars, new entrants undercutting), and firms may collude instead. The most defensible conclusion is that non-price competition is generally preferred in oligopoly because of interdependence and the risk of price wars, but the choice depends on the strength of brand loyalty, the threat of entry, and whether firms collude or compete.