Cournot Competition vs Bertrand Competition
Cournot Competition and Bertrand Competition are two Market Structures concepts in AP Economics that students often mix up. Cournot competition is an oligopoly model where firms simultaneously choose how much quantity to produce, and the combined output sets the market price. Bertrand competition is an oligopoly model where firms simultaneously set prices, and consumers buy from whoever charges less. Here is how they compare side by side.
Each firm picks its output taking rivals' outputs as given, and equilibrium occurs where their reaction functions intersect (a Nash equilibrium in quantities). The result lies between monopoly and perfect competition: price exceeds marginal cost and firms earn positive profit, but less than a monopolist would. As the number of firms rises, the outcome approaches the competitive one.
With identical products and equal constant costs, price competition drives firms to undercut each other until price equals marginal cost, giving the competitive outcome and zero economic profit even with only two firms, the Bertrand paradox. The result is sensitive to assumptions: product differentiation, capacity limits, or repeated play restore positive profits.
Cournot vs Bertrand: One Duopoly, Two Strategic Variables, Two Prices
| Cournot Competition | Bertrand Competition | |
|---|---|---|
| What each firm chooses | A quantity to produce, taking the rival's quantity as given | A price to post, taking the rival's price as given |
| How the price gets set | By the market, once combined output meets demand | By the firms directly, and the lower price takes the market |
| Equilibrium with two identical firms | Price above marginal cost, output between the monopoly and competitive levels | Price down at marginal cost and zero profit from only two sellers, the Bertrand paradox |
| Who serves the buyers | Both firms, in equal shares when their costs match | The cheaper firm alone, with an even split only if the prices tie |
| Effect of adding a third firm | Price falls another step toward marginal cost | No effect, price already sits at marginal cost |
| When the model fits | Capacity is committed before sale, as with crops, cement or airline seats | Output scales up quickly and buyers see the goods as identical |
| What changes the result | Differing costs shift each firm's share, but price stays above MC | Capacity limits, product differentiation or repeated play lift price back above MC |
Run the numbers and the two models disagree by eight dollars
Take market demand of P equals 30 minus Q, two firms, and constant marginal cost of $6 each. Under Cournot, each firm picks output while treating the rival's output as fixed, and the reaction functions meet where each produces 8 units. Combined output is 16, price is $14, and each firm earns an $8 margin on 8 units for a profit of $64. Under Bertrand, each firm posts a price, and any price above $6 invites the rival to shave a cent and take the entire market. The only resting point has both firms pricing at $6, selling 24 units between them and earning nothing. Same demand curve, same costs, same two firms, and the predicted price moves from $14 to $6. For reference, a monopolist facing this demand would produce 12 units at a price of $18. The strategic variable, not the number of competitors, is doing the work.
The Bertrand zero-profit result rests on assumptions that rarely all hold
Two firms driving price down to marginal cost is a striking prediction, and it is fragile. The result needs identical products, so no buyer will pay extra for a brand. It needs constant marginal cost with no capacity ceiling, so the winner can serve every customer at once. It needs a single simultaneous move, so nobody fears retaliation tomorrow. Relax any one of those and price lifts off marginal cost. Give each firm capacity that covers only part of the market and the loser of the price war still sells to customers the winner cannot serve, so undercutting stops paying and the outcome drifts toward the Cournot prediction. Differentiate the products and each firm keeps loyal buyers even while charging more. Repeat the game and the threat of a lasting price war can support prices near the collusive level. The paradox earns its keep less as a forecast than as a checklist of which assumption a real market violates.
Neither name is required vocabulary, but the idea behind them is
AP Microeconomics builds its oligopoly unit on payoff matrices, dominant strategies and Nash equilibrium rather than on these two named models, so a question will hand you a grid instead of asking for a reaction function. The distinction still earns its place, because it explains something the grids leave unsaid. When the strategies in a matrix are output levels, the cooperative cell pays well and the equilibrium cell still shows positive profit, which is the Cournot flavor. When the strategies are prices and the goods are identical, the equilibrium cell can show almost nothing for either firm, which is the Bertrand flavor. In a college intermediate micro course these become the standard duopoly workhorses and you solve them with algebra. For now the takeaway is that oligopoly carries no single price prediction. What the firms compete over decides how much market power a small number of sellers actually delivers.
Frequently asked questions
Why does Bertrand competition give the competitive price with only two firms?
Price undercutting drives the result. If a rival posts any price above marginal cost, a firm can set a price a fraction lower and capture the entire market instead of half of it, and the extra volume outweighs the thinner margin. Both firms see that, so any price above marginal cost gets undercut. Pricing below marginal cost loses money on every unit sold. The only pair of prices where neither firm wants to move is both at marginal cost. Two firms suffice because the goods are identical and either can supply everyone.
Which model describes real oligopolies better?
Neither model wins outright, and the useful question is which assumption fits the industry in front of you. Cournot suits markets where output is committed before it is sold and capacity is expensive to change, such as mining, farming and heavy manufacturing. Bertrand suits markets where a seller can fill any order immediately and buyers compare identical items on price, which is closer to online retail of standardized goods. A common compromise has firms choose capacity first and price second, and that two-stage setup reproduces the Cournot outcome, one reason Cournot predictions get quoted more often.
Do firms in Cournot competition earn monopoly profits?
Cournot duopolists earn less than a monopolist would and more than perfect competitors do. Each firm ignores the damage its extra output does to the rival's revenue, so combined output lands above the level the two would pick jointly and price lands below the monopoly price. In the demand example above, joint monopoly profit would be $144 while the Cournot pair splits $128. Adding firms widens that gap, and as the number of firms grows large the Cournot price converges on marginal cost.
Related comparisons
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