Market Power

Market power is the ability to set price above marginal cost without losing so much volume that the move destroys value. In perfect competition, price equals marginal cost and economic profit is zero. Any firm that can charge more and hold volume has market power. The source of that power is always the same: the buyer has no good alternative. Few substitutes, high switching costs, necessity, regulation, or information asymmetry — each reduces the buyer's ability to walk away. The firm with market power faces a downward-sloping demand curve. It chooses a point on that curve. Competitors take price; firms with market power make it.

The degree of market power varies. A monopolist faces the entire market demand curve and maximises where marginal revenue equals marginal cost. Duopolists and oligopolists face residual demand — what's left after rivals supply their quantity. The less elastic that residual demand, the more power. Concentration alone doesn't guarantee power; the key is whether customers can substitute. A concentrated industry with a close substitute from another sector has less power than the concentration numbers suggest. A fragmented industry where each player has loyal customers and high switching costs can support sustained margins. The diagnostic is always: if this firm raised price 10%, how much volume would it lose? Low loss means power.

Antitrust and industrial organisation define market power formally. The Lerner Index — (P − MC) / P — measures the price-cost margin as a fraction of price. Zero means no power; 0.3 means price is 43% above marginal cost. In practice, firms rarely know their marginal cost precisely, and the relevant "market" is often contested. The strategic question is simpler: can we raise price without volume collapsing? Can we sustain that margin against entry and substitution? Market power that attracts entry is temporary. Sustainable power requires barriers that prevent substitutes from emerging or competitors from scaling.

In competitive strategy, market power is the flip side of differentiation. The more differentiated the product — in fact or in perception — the fewer close substitutes and the steeper the demand curve. Commodity businesses have no power; they compete on cost and volume. The goal of strategy in most industries is to create or protect a segment where you have some power, then price and invest accordingly. Ignoring the power question leads to either leaving money on the table (if you have power and don't use it) or grinding margin in a commodity trap (if you don't have power and assume you do).