Contestable market

A market with only one or two firms might still behave competitively, if the threat of entry is real enough. That insight is the theory of contestable markets.

A contestable market is one in which the threat of entry is enough to discipline the behaviour of existing firms, so that even a market with few competitors can produce competitive outcomes. The theory holds that what matters is not how many firms are actually in a market but how easily others could enter and leave.

Potential competition as discipline

The central claim is that potential competition can be as powerful as actual competition. If entry into a market is easy and exit is costless, so that a newcomer could swoop in to undercut any firm earning excess profits and leave again without loss, then incumbents dare not raise prices above the competitive level, even if there are only one or two of them. The mere possibility of hit-and-run entry keeps them honest. The market is disciplined not by the rivals present but by the rivals who could appear.

The condition that makes it work

Contestability depends crucially on the absence of sunk costs, the costs of entry that cannot be recovered on exit. If entering a market requires large irreversible investments, potential entrants are deterred, because they cannot swoop in and out without risk, and the threat of entry loses its force. So a market is contestable only when entry and exit are genuinely easy and cheap, with assets that can be redeployed or resold. Where sunk costs are high, even a market that looks open is not truly contestable.

Implications and limits

The theory has important implications: it suggests competition policy should focus on keeping entry easy and removing sunk-cost barriers rather than fixating on the number of firms, and that a concentrated market need not be a problem if it is contestable. But its strict conditions, costless entry and exit, no sunk costs, are rarely fully met, since most real markets involve some irreversible investment. So perfect contestability is, like perfect competition, an idealisation, valuable as a benchmark and a guide to policy more than a description of reality.

Contestable market theory shifts the focus from the firms in a market to the ease with which others could join it, arguing that the threat of entry can discipline even a concentrated industry. Its lesson, that potential competition matters and that sunk costs are the real barrier, has shaped how economists and regulators think about competition, even where its demanding conditions do not fully hold.