Questions: Monopoly: Sources of Market Power and Barriers to Entry

Question 1

A single firm earns very high profits and has 90% market share in an industry. A new competitor could profitably enter using identical technology and without needing any special permits. Does this firm have a durable monopoly?

• A. Yes — 90% market share demonstrates monopoly power by definition
• B. Yes — high profits prove the firm has pricing power above competition
• C. No — without a barrier to entry, high profits will attract new entrants who erode the market share and profits over time
• D. No — monopoly requires 100% market share, so 90% is by definition not a monopoly

Answer: (C)

Market share and current profits alone do not create a durable monopoly — only barriers to entry do. In this scenario, any firm can enter using the same technology without legal restrictions. High profits are a signal to potential entrants that the market is attractive. Without a barrier that prevents them from entering, competition will erode both the market share and the above-normal profits until they reach competitive levels. Monopoly is fundamentally about the durability of market power, which requires something specific blocking entry.

Question 2

A pharmaceutical company holds a patent on a blockbuster drug and earns large profits. Which type of barrier to entry explains this monopoly, and what happens to the barrier's effectiveness over time?

• A. Natural monopoly due to economies of scale; it becomes stronger as the company grows
• B. Exclusive input control; it weakens as the patent expires and generic manufacturers copy the formula
• C. Legal barrier (patent); it is fixed-term and expires, after which competitors can legally enter
• D. Network effects; it strengthens over time as more patients use the drug

Answer: (C)

Patents are legal barriers created by law that grant temporary exclusive rights. They are explicitly time-limited (typically 20 years from filing) and designed to balance innovation incentives with eventual competition. When a patent expires, generic manufacturers can enter the market with identical molecules, typically causing dramatic price drops. This distinguishes patents from natural monopoly (cost structure-based) or network effects (self-reinforcing user base) — legal barriers do not depend on the technology or economics but on the legal framework, which can change.

Question 3

A natural monopoly arises because a single firm can produce the entire market output at lower average cost than two or more competing firms.

• T. True
• F. False

Answer: True

Natural monopoly is defined by the cost structure of the industry, specifically by economies of scale that persist over the full range of market demand. When average costs are still falling at the output level where the market is satisfied, splitting production between multiple firms forces each to operate at inefficiently small scale, raising average costs above what the single large firm achieves. Utilities (water, electricity transmission) are classic examples: the infrastructure cost is so large that duplicating it is wasteful. This is why natural monopolies are often regulated rather than simply broken up — the economic logic favors single-firm production even if the price outcome requires oversight.

Question 4

Network effects function as a barrier to entry because they make the incumbent's product technically superior to any new entrant's product.

• T. True
• F. False

Answer: False

Network effects create a barrier through user base size, not technical superiority. The incumbent's product may be technically identical or even inferior to a new entrant's product, but users still prefer it because it has more users — more people to message, more sellers to buy from, more merchants that accept the payment. A new entrant with a better product but a small network offers less value to any individual user. This makes switching costly and entry difficult even when the challenger's technology is demonstrably better. The barrier is the installed base, not the product quality.

Question 5

Why is 'barriers to entry' the central concept in defining monopoly, rather than simply market share or firm size?

Model answer: Market share and size can arise temporarily through innovation, luck, or efficiency, but without barriers they are eroded by competition. In a competitive market, any firm earning above-normal profits sends a signal to potential entrants: 'this industry is worth entering.' Firms will enter until profits are driven to normal competitive levels. Monopoly persists only when some mechanism — exclusive input control, legal barriers, economies of scale, or network effects — prevents this entry mechanism from working. The barrier is what converts a temporarily dominant firm into a permanent monopoly. Without it, market power is fleeting; with it, market power can be sustained indefinitely (or until the barrier itself erodes through technological change).

This perspective also explains why antitrust analysis focuses on barriers: regulators trying to promote competition don't need to directly attack a firm's market share — they need to remove or reduce the barrier that prevents new entry. Lowering barriers (shortening patent terms, regulating essential infrastructure access, preventing exclusive dealing contracts) can restore competitive pressure without directly restructuring the dominant firm.