contestables

Contestables, in economics, refers to markets whose competitiveness is determined by the ease with which new entrants can challenge incumbents, not merely by how many firms currently operate. The concept, formalized by William Baumol, John Panzar, and Robert Willig in 1982, argues that the threat of entry and exit can discipline prices even in markets with few firms, provided entry and exit are inexpensive.

Core conditions include low or zero sunk costs, minimal barriers to entry and exit, access to essential inputs, and reasonably available information. When these conditions hold, potential entrants can enter to capture profits if incumbents charge above the competitive price, driving prices toward marginal cost and profits toward zero in the long run.

In practice, contestability is partly constrained by real-world frictions such as sunk costs, regulatory barriers, capital requirements, network effects, and strategic behavior. As a result, markets with few firms can still exhibit imperfect competition if entry is difficult, while some highly concentrated markets can appear contestable if entry is easy.

Applications and policy relevance focus on sectors where regulation shapes entry costs—utilities, transportation, and professional services—as well as platforms where digital access lowers barriers. The framework informs competition policy by highlighting that preventing entry barriers can be as important as increasing the number of competitors.

Limitations include reliance on strong assumptions (transparent information, constant returns to scale) and challenges in empirical testing. Nonetheless, the contestable markets perspective remains a foundational tool in industrial organization for understanding how potential entry shapes market outcomes.