Contestable Markets

The theory of contestable markets was developed by William Baumol, John Panzar, and Robert Willig (1982) in their seminal work Contestable Markets and the Theory of Industry Structure. The theory transformed the way economists think about competition by arguing that what matters for competitive outcomes is not the number of firms in a market, but the threat of potential entry. A market can deliver competitive outcomes even with very few firms, provided the market is contestable.

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What Makes a Market Contestable?

A market is perfectly contestable if:

Condition	Explanation
No barriers to entry	New firms can enter the market freely, without facing legal, technical, or strategic obstacles
No barriers to exit	Firms can leave the market freely — crucially, they can recover all their investment (no sunk costs)
No sunk costs	All costs can be recovered if the firm exits — the firm can sell its assets, terminate leases, and exit without financial loss
Access to the same technology	Potential entrants have access to the same production technology as incumbents — no technological advantage for existing firms
Perfect information	Potential entrants are fully aware of the profit opportunities available in the market

The Central Insight

In a perfectly contestable market, the threat of entry is sufficient to discipline incumbents. Even a monopolist or oligopolist will behave competitively — charging prices close to average cost and earning only normal profit — because any supernormal profit would attract "hit-and-run" entrants.

Exam Tip: The key distinction from traditional models is that contestability focuses on potential competition rather than actual competition. A market with only one firm can still be competitive if it is contestable. This is a fundamental shift in thinking about market structure and competition policy.

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Sunk Costs: The Key Barrier

Sunk costs are costs that cannot be recovered when a firm exits a market. They are the single most important factor determining the contestability of a market.

Cost Type	Recoverable?	Example	Effect on Contestability
Non-sunk costs	Yes — can be sold or reused	Vehicles that can be resold, leased office space that can be terminated	Increases contestability
Sunk costs	No — lost if the firm exits	Advertising expenditure, specialist equipment with no resale value, regulatory compliance costs	Reduces contestability

Why Sunk Costs Matter

If sunk costs are zero, a potential entrant faces no risk from entering the market:

• If the market is profitable, the entrant earns profit
• If the market turns unprofitable, the entrant exits and recovers all costs — no loss

This makes entry costless and exit painless, creating the conditions for hit-and-run entry.

Exam Tip: The relationship between sunk costs and contestability is inverse: the higher the sunk costs, the less contestable the market. When evaluating whether a market is contestable, always identify the level of sunk costs — this is the most important single factor.

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Hit-and-Run Entry

Baumol's model of hit-and-run entry describes how potential entrants can discipline incumbents:

1. An incumbent firm earns supernormal profit
2. A potential entrant observes the profit opportunity
3. The entrant enters the market, undercuts the incumbent's price slightly, and captures market share
4. The entrant earns profit for as long as the opportunity persists
5. If the incumbent responds by cutting prices, the entrant exits the market without loss (because there are no sunk costs)

The threat of this process is sufficient to prevent incumbents from charging supernormal prices in the first place. The incumbent sets prices at the competitive level pre-emptively, even without any actual entry occurring.

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Limit Pricing

Limit pricing is a strategy used by incumbent firms to deter potential entrants. The incumbent sets its price below the level that would maximise short-run profit but above the level that a potential entrant could profitably match, given the entrant's cost disadvantage.

Feature	Explanation
Purpose	To make entry unprofitable for potential competitors
Price level	Below the profit-maximising price but above the competitive price — the incumbent sacrifices some short-run profit to protect its market position
Effectiveness	Depends on whether the incumbent's threat is credible and whether the entrant believes the low price will persist after entry
Risk	The incumbent earns less than it could in the short run; if the threat of entry is not real, the limit pricing is unnecessarily costly

Limit Pricing vs Predatory Pricing

Feature	Limit Pricing	Predatory Pricing
Timing	Before entry — to deter	After entry — to drive out
Price level	Above cost (but below monopoly price)	Below cost (temporarily)
Legality	Generally legal	Illegal if it constitutes abuse of a dominant position (Competition Act 1998, Chapter II)
Duration	Sustained — the incumbent keeps prices low permanently	Temporary — the predator intends to raise prices after the rival exits

Exam Tip: Distinguish clearly between limit pricing and predatory pricing. Students often confuse them. Limit pricing is a pre-entry deterrent that involves pricing above cost. Predatory pricing is a post-entry strategy that involves pricing below cost. The CMA investigates predatory pricing as potential abuse of dominance, but limit pricing is generally not considered anti-competitive.

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