Prisoner's dilemma

Topic: Market Structures, Market Failure and Competition · NCERT: Beyond NCERT

Meaning

The prisoner's dilemma is a game in which each player's dominant strategy (the best choice whatever the other does) is to defect (break cooperation). When both defect, the result is a Nash equilibrium that is worse for both players than if they had cooperated.

• Payoff condition: Temptation > Reward > Punishment > Sucker's payoff. In the cement example below this is 15 > 10 > 5 > 2.
• Temptation is what you get by cheating while the rival cooperates.
• Reward is what each gets when both cooperate.
• Punishment is what each gets when both cheat.

• Sucker's payoff is what you get by cooperating while the rival cheats.

• Why it matters: it shows that choices that are rational for each person can give a bad result for the group. It explains why cartels are unstable, and it also explains arms races, tariff wars, climate deadlock and over-fishing.

Explanation

How the game works: the cement cartel

• Players: two cement firms, A and B.
• Strategies: keep the high cartel price, or cut the price.

• A cartel is a group of firms that agree to fix prices, limit output or share markets instead of competing.

• Payoffs: profit in ₹ crore, written as (A, B).

	B: Keep high price	B: Cut price
A: Keep high price	(10, 10)	(2, 15)
A: Cut price	(15, 2)	(5, 5)

• Step 1: find A's best reply.
• If B keeps the high price, A gets 15 by cutting and 10 by keeping. Cutting is better.
• If B cuts, A gets 5 by cutting and 2 by keeping. Cutting is better again.

• So cutting is A's dominant strategy.

• Step 2: B's best reply. The game is the same for both firms, so cutting is B's dominant strategy too.

• Step 3: the equilibrium is (Cut, Cut) = (5, 5).

• If A alone switches back to Keep, A gets 2, which is less than 5. B faces the same choice. So neither firm moves.

• Step 4: compare this with cooperation.

• (Keep, Keep) = (10, 10) is better for both firms. Joint profit is 20 under cooperation and only 10 in the equilibrium.

• But (Keep, Keep) does not last. Each firm gains 15 − 10 = ₹5 crore by cheating. This temptation is what breaks cartels.

• Lesson: each firm makes a rational choice, and together they get a result that is bad for both.

Key ideas inside the dilemma

• Dominant strategy: a choice that is best whatever the rival does. In the prisoner's dilemma, "defect" is dominant for both players.
• Nash equilibrium: a set of choices where no player can gain by changing strategy alone, given what the others are doing. It is named after John Nash (1950).
• It need not be efficient. Pareto-efficient means no other outcome can make someone better off without making anyone worse off. (Cut, Cut) is a Nash equilibrium, but (Keep, Keep) makes both firms better off.

• If every player has a dominant strategy, those strategies together form a Nash equilibrium. The reverse is not always true.

• Not a zero-sum game. In a zero-sum game, one side's gain equals the other side's loss. Here the total payoff changes with the choices: 20 in (Keep, Keep) and 10 in (Cut, Cut).

• Non-cooperative game: the players cannot sign agreements that a court would enforce, so each decides alone. That is why a promise to "keep the price high" cannot be trusted.
• Origin: Merrill Flood and Melvin Dresher first framed the game around 1950 [6]. Nash, Harsanyi and Selten won the 1994 Nobel Prize in Economics for their "pioneering analysis of equilibria in the theory of non-cooperative games" [5].
• The consumer's view: the equilibrium that is "bad" for the firms means low prices, which is good for buyers. Competition law tries to keep firms in this equilibrium.

What weakens or strengthens the dilemma: repeated games

• One-shot game: the game is played once, and defection wins.
• Repeated game: the same game is played again and again. The threat of future punishment can keep players cooperating.
• Worked example (cement matrix, 3 rounds, no discounting):
• Always cooperate: 10 + 10 + 10 = 30.
• Cheat in round 1, after which the rival cuts forever: 15 + 5 + 5 = 25.

• Since 30 > 25, cheating does not pay once punishment is expected. Over 10 rounds the gap grows to 100 vs 60.

• Catch: the known last round.

• If both firms know which round is the last, both cheat in it.
• Working backwards, cooperation falls apart round by round.

• So cooperation lasts only when the end is uncertain or never comes.

• Tit-for-tat: cooperate in the first round, then copy what the rival did last.

• In 1980, Robert Axelrod ran tournaments in which computer programs played repeated prisoner's dilemmas with no fixed end. Tit-for-tat won [6].

• It works because it is nice (it never cheats first), retaliatory (it punishes cheating at once), forgiving (it cooperates again as soon as the rival does) and clear (the rival can easily understand it).

• Tacit collusion: in stable oligopolies, repeated play lets firms keep prices high without any written or spoken agreement.

• An oligopoly is a market with a few large sellers, such as cement, telecom or tyres.
• Tacit collusion lasts where there are few firms, prices are easy to see and the market is stable.

Where else the dilemma appears

• Arms races: arming is each country's dominant strategy. Both spend heavily, and neither is safer.
• Tariff wars: each country gains a little by protecting its own industry. When both do it, trade shrinks and both lose, as in the US-China tariff rounds.
• Climate talks: each country prefers that others cut emissions. This is free riding (enjoying a benefit without paying for it) on a global public good.

• A public good is non-excludable (no one can be stopped from using it) and non-rival (one person's use does not reduce what others get).

• Fisheries (tragedy of the commons): each boat keeps the full gain from an extra catch, but the loss of fish is shared by everyone. So every boat over-fishes and the fishery collapses.

In India

• Cartels are illegal: Section 3 of the Competition Act, 2002 covers them.
• Section 3(1) bans anti-competitive agreements.

• Section 3(3) covers horizontal agreements (agreements between rivals), including bid-rigging under Section 3(3)(d) [4].

• The regulator: the Competition Commission of India (CCI) enforces the Act. It investigated 35 cartel cases in the five years covered by a 2025 PIB release [1].

• Leniency (lesser penalty) uses the prisoner's dilemma on purpose:
• The legal basis is Section 46 of the Act, read with the CCI (Lesser Penalty) Regulations [1].
• The first firm to report the cartel gets the biggest cut in its penalty. This makes "confess first" the dominant strategy, so the cartel breaks up.
• The CCI (Lesser Penalty) Regulations, 2024 were notified on 20 February 2024. They replaced the 2009 regulations [1].

• The Competition (Amendment) Act, 2023 added "Lesser Penalty Plus" (LPP). A firm that has already applied for leniency in one cartel gets an extra penalty cut if it reports another cartel that the CCI did not know about [1]. This turns every cartel a firm belongs to into a possible confession game.

• The race to confess in real cases:

Case	1st applicant	2nd	3rd
Zinc-carbon dry cell batteries	Panasonic: 100% reduction	Eveready: 30%	Nippo: 20% [2]
Maritime transport (car carriers)	NYK Line: 100%	MOL: 50%	NMCC: 30% [3]

• Cement bid-rigging: the CCI penalised 7 cement companies for bid-rigging in a 2012 tender floated by the Director, Supplies & Disposals, Haryana [4].
• The penalties included UltraTech (₹68.30 crore), Jaiprakash Associates (₹38.02 crore), ACC (₹35.32 crore) and Ambuja (₹29.84 crore) [4].
• Each penalty was 0.3% of average turnover over the preceding three years [4].
• The violation was Section 3(3)(d) read with Section 3(1) [4].

Don't confuse with

• Zero-sum game: in a zero-sum game, one side's gain exactly equals the other's loss, as in poker. In the prisoner's dilemma, the total payoff changes with the choices (20 vs 10), so it is not zero-sum.
• Pareto-efficient outcome: the Nash equilibrium of the prisoner's dilemma (Cut, Cut) is not Pareto-efficient, because (Keep, Keep) makes both players better off.
• Tacit collusion: a one-shot prisoner's dilemma ends in defection. Tacit collusion is cooperation that survives through repeated play, with no explicit agreement.
• Positive-sum game (voluntary trade): both sides gain because a bigger total is created. The prisoner's dilemma also has a cooperative outcome with a bigger total, but self-interest stops the players from reaching it.

Prelims Hooks

• In the prisoner's dilemma, "defect" (cut price or confess) is the dominant strategy for both players, and (Defect, Defect) is the Nash equilibrium.
• A Nash equilibrium means no player gains by changing strategy alone. It need not be Pareto-efficient, which is a common trap.
• The prisoner's dilemma is NOT a zero-sum game.
• The 1994 Nobel Prize in Economics went to Nash, Harsanyi and Selten for equilibria in non-cooperative games [5]. Flood and Dresher first framed the game around 1950 [6].
• Tit-for-tat (cooperate first, then copy the rival) won Axelrod's 1980 tournaments of repeated prisoner's dilemmas [6].
• India's leniency regime is Section 46, Competition Act, 2002 with the CCI (Lesser Penalty) Regulations, 2024 [1]. Lesser Penalty Plus came from the 2023 amendment [1]. Bid-rigging falls under Section 3(3)(d) [4].

Mains Points

• Competition policy uses cartel instability (GS-III):
• Cheating is each cartel member's dominant strategy.
• India's lesser penalty regime (Section 46, the 2024 Regulations and LPP) makes staying silent a losing strategy [1].
• Graded rewards (100% / 50% / 30% in the maritime case) start a race to confess [3].

• The limit is tacit collusion in concentrated sectors such as cement. It keeps prices high without an agreement that can be proved under Section 3. Possible fixes are market studies, price-transparency rules, scrutiny of mergers and evidence from leniency applicants.

• Global commons and trade (GS-II and GS-III):

• Climate talks and tariff wars show self-interested nations ending up in bad equilibria.

• The WTO (the MFN rule, under which a country must treat all WTO members equally on tariffs, plus binding tariff ceilings and dispute settlement) and the UNFCCC (national pledges with review) act as "repeated game" devices. They reward cooperation and make cheating visible.

• Individual rationality vs social efficiency:

• Over-fishing and arms races show that a Nash equilibrium can be rational for each player yet wasteful for society.
• This is a key argument for state regulation when markets fail, through quotas, pollution standards and competition law, instead of relying on the market alone.

Related concepts

• Game theory
• Zero-sum game
• Positive-sum game
• Dominant strategy
• Nash equilibrium

Read more

• Game theory: strategic interaction