Comparison of market structures: key differences in number of firms, product differentiation, entry barriers, pricing power, and equilibrium outcomes.
## Core concept
A market structure is defined by the number of firms, nature of products, and ease of entry/exit. The four main structures—perfect competition, monopolistic competition, oligopoly, and monopoly—differ fundamentally in competitive intensity and firm behavior. Understanding these differences is essential for analyzing pricing, output, and profit outcomes.
## Key distinguishing features
| Feature | Perfect Competition | Monopolistic Competition | Oligopoly | Monopoly | |---------|---|---|---|---| | Number of firms | Many | Many | Few | One | | Product type | Homogeneous | Differentiated | Homogeneous or differentiated | Unique (no close substitutes) | | Entry barriers | None/Low | Low | High | Very high | | Pricing power | None (price taker) | Some (brand loyalty) | Significant (interdependent) | High (price maker) | | Long-run profit | Zero (normal profit only) | Zero (due to entry) | Positive (barriers protect) | Positive | | Demand curve | Perfectly elastic (horizontal) | Downward-sloping | Kinked (oligopoly) or varies | Downward-sloping (market demand) | | Price vs. marginal cost | P = MC | P > MC | P > MC | P > MC |
## Equilibrium comparison
- Perfect Competition: Firms produce where P = MC. Long-run: P = AC (zero supernormal profit); allocatively and productively efficient.
- Monopolistic Competition: Firms produce where MR = MC, but P > MC. Long-run: P = AC (zero supernormal profit); productive inefficiency due to excess capacity.
- Oligopoly: Firms produce where MR = MC; P > MC. Long-run profit possible due to barriers; output lower, price higher than perfect competition; kinked demand curve reflects price rigidity.
- Monopoly: Single firm produces where MR = MC; P > MC. Long-run supernormal profit; allocatively inefficient (underproduction); may earn economic rent.
## Common exam applications
- Identifying market structure: Given number of firms, product nature, and entry conditions, classify and explain equilibrium.
- Price and output analysis: Compare monopolist vs. competitive firm output under identical cost conditions (monopoly produces less at higher price).
- Efficiency assessment: Perfect competition achieves allocative and productive efficiency; monopoly fails both; monopolistic competition fails productive efficiency.
- Interdependence in oligopoly: Firms' decisions depend on rivals' reactions; price wars or collusion may result.
## Worked example
Question: A market has 50 firms producing identical light bulbs with identical cost structures (AC = Rs. 5, MC = Rs. 5). Under perfect competition, the market price is Rs. 5. If one firm merges with 49 others to form a monopoly, the demand curve is P = 20 − 0.5Q. The monopoly's MC remains Rs. 5. Compare output and profit.
Solution: - Perfect competition: P = MC = Rs. 5; each firm produces where MR = P = 5. If market output is 10,000 units, each firm produces 200 units; profit = 0 (P = AC). - Monopoly: MR = 20 − Q. Setting MR = MC: 20 − Q = 5 → Q = 15. Price: P = 20 − 0.5(15) = Rs. 12.5. Profit per unit = 12.5 − 5 = Rs. 7.5; total profit = Rs. 112.5 (positive).
Result: Monopoly restricts output from 10,000 to 15 units (assuming demand scale), raises price, and earns supernormal profit—allocative inefficiency.
## Common mistakes
- Assuming all non-competitive markets have identical behavior; oligopolies are unpredictable (game theory applies).
- Forgetting that long-run zero profit in monopolistic competition occurs despite downward-sloping demand (entry erodes profit).
- Conflating monopoly with high prices; monopoly maximizes profit, not price (price is outcome, not goal).
- Missing that kinked demand (oligopoly) explains price rigidity, not equilibrium directly.