Chapter 18 showed you the world where competition works perfectly: many firms, identical products, free entry, zero economic profit. Now we look at the opposite extreme: one firm, no close substitutes, and barriers that prevent other firms from...
Learning Objectives
- Identify four sources of monopoly power and give examples of each.
- Show graphically how a monopolist sets quantity and price, and calculate the deadweight loss.
- Distinguish first-, second-, and third-degree price discrimination with real examples.
- Evaluate whether contemporary tech firms qualify as monopolies and what should be done.
In This Chapter
Chapter 19 — Monopoly
When One Firm Controls the Market
Chapter 18 showed you the world where competition works perfectly: many firms, identical products, free entry, zero economic profit. Now we look at the opposite extreme: one firm, no close substitutes, and barriers that prevent other firms from entering. This is monopoly — and it produces outcomes that are starkly different from the competitive benchmark.
A monopolist faces no competitors. It is the sole supplier of a product for which no good substitute exists. This gives it market power: the ability to set a price above marginal cost and earn persistent economic profit. The market power is not free — it comes at a cost to consumers (higher prices) and to society (deadweight loss). Understanding how monopoly works, why it persists, and what to do about it is one of the central tasks of microeconomics.
By the end of this chapter, you should be able to identify the sources of monopoly power, draw the monopolist's profit-maximizing diagram, calculate the deadweight loss, analyze price discrimination, and evaluate the most important contemporary monopoly debate: whether Big Tech firms like Google, Apple, Amazon, and Meta are monopolies — and whether antitrust law should do something about them.
19.1 Sources of monopoly power
Why do some markets have only one firm? Four main reasons.
1. Legal barriers to entry
The government grants exclusive rights to produce a good. The most common form is a patent: a 20-year exclusive right to produce an invention. Pharmaceutical companies earn monopoly profits on patented drugs because no competitor can produce the same drug until the patent expires. Other legal barriers include government-granted licenses (your local cable franchise, many utility companies) and copyrights (exclusive right to reproduce creative works).
Why legal barriers exist: patents and copyrights exist to incentivize innovation. Without the promise of temporary monopoly profits, firms would invest less in R&D because competitors could immediately copy their inventions. The social tradeoff: temporary monopoly power (inefficient) in exchange for more innovation (efficient in the long run).
2. Natural monopoly
A natural monopoly exists when a single firm can supply the entire market at a lower average cost than two or more firms could. This happens when fixed costs are very high relative to variable costs and the market is not large enough to support multiple firms at efficient scale.
Classic examples: water utilities (one set of pipes is much cheaper than two), electricity transmission (one grid is more efficient than competing grids), railroads (one track between two small cities is enough).
The economic logic: if ATC declines over the relevant range of output (economies of scale that don't run out), then one firm producing the entire market's output has lower ATC than two firms each producing half. Competition would actually be more expensive.
The policy challenge: natural monopolies can't be fixed by encouraging competition (competition would raise costs). They have to be regulated — either by a government price regulator (which sets the price the monopolist can charge) or by government ownership (the government operates the utility directly).
3. Network effects
A network effect exists when the value of a product increases as more people use it. A telephone is useless if only one person has one; it becomes valuable as millions of people join the network. Social media platforms, messaging apps, payment systems, and operating systems all exhibit network effects.
Network effects create monopoly because once one firm achieves critical mass (enough users that the network is valuable), it becomes very hard for a competitor to attract users away. Why would you switch from the dominant social network (where all your friends are) to a new one (where no one is)? The switching cost is not monetary — it's the loss of the network.
Examples: Google dominates search (about 90% market share globally). Facebook/Instagram/WhatsApp dominate social media. Amazon dominates e-commerce. Each benefits from network effects that make it very hard for competitors to gain traction.
4. Control of essential inputs
If a firm controls an input that competitors need and can't get elsewhere, the firm has a monopoly. De Beers historically controlled a large share of the world's diamond supply. OPEC members collectively control a large share of oil supply (though OPEC is a cartel, not a single firm). Some rare-earth mineral deposits are controlled by a small number of producers.
19.2 The monopolist's pricing decision
A monopolist faces the entire market demand curve — unlike a competitive firm (which faces a horizontal line at the market price). This means the monopolist has to choose how much to produce. And because the demand curve slopes down, producing more means accepting a lower price.
Marginal revenue for a monopolist
For a competitive firm, MR = P (selling one more unit doesn't change the price). For a monopolist, MR < P. Why? Because to sell one more unit, the monopolist has to lower the price on all units — not just the marginal one.
Numerical example: suppose the monopolist faces demand: P = 100 − Q.
| Q | P | TR (P×Q) | MR (ΔTR/ΔQ) |
|---|---|---|---|
| 0 | 100 | 0 | — |
| 10 | 90 | 900 | 90 |
| 20 | 80 | 1,600 | 70 |
| 30 | 70 | 2,100 | 50 |
| 40 | 60 | 2,400 | 30 |
| 50 | 50 | 2,500 | 10 |
| 60 | 40 | 2,400 | −10 |
Notice: MR falls twice as fast as P. At Q = 50, MR = 10 (much less than P = 50). At Q = 60, MR is actually negative — producing more reduces total revenue. The monopolist would never produce in the negative-MR range.
For a linear demand curve P = a − bQ, the MR curve has the same intercept but twice the slope: MR = a − 2bQ.
Profit maximization: MR = MC
The monopolist maximizes profit by producing where MR = MC — the same rule as Chapter 18, but with MR < P instead of MR = P. The monopolist then charges the price that the demand curve says consumers are willing to pay for that quantity.
MONOPOLY PRICING
Price /
Cost
$100 |\
| \
| \ Demand
$80 | \
| \
$70 | ★ ← Monopoly price (Pm)
| |╲
$60 | | ╲
| | ╲ MC
$50 | | ╱╲
| | ╱ ╲
$40 | | ╱ ★ ╲ ← MC at monopoly quantity
| |╱ (MR=MC) ╲
$30 | ★ ╲
| ╱| MR ╲
$20 | ╱ | ╲
|╱ | ╲
$10 | | ╲
| | ╲
|____|____________________________╲_
0 Qm Qc Quantity
↑ ↑
Monopoly Competitive
quantity quantity (where MC = Demand)
Figure 19.1 — Monopoly pricing. The monopolist produces Qm (where MR = MC) and charges Pm (the price consumers are willing to pay at Qm, read from the demand curve). The competitive outcome would be Qc (where MC = Demand, i.e., P = MC). The monopolist produces less and charges more than competition would.
The deadweight loss of monopoly
The monopolist produces Qm instead of the competitive quantity Qc. The units between Qm and Qc are units that consumers value more than they cost to produce (the demand curve is above the MC curve in that range). These trades would happen in a competitive market but don't happen under monopoly. The lost value — the surplus that would have been created by those trades — is the deadweight loss of monopoly.
The deadweight loss is the triangle between the demand curve and the MC curve, from Qm to Qc. It's the same concept as the deadweight loss from a tax (Chapter 7) or a price control (Chapter 7) — value destroyed by the gap between what happens and what would be efficient.
Monopoly profit
The monopolist's profit is the rectangle: (Pm − ATC) × Qm. This is economic profit — above and beyond the normal return. Unlike in perfect competition (where entry drives profit to zero), the monopolist can sustain positive economic profit indefinitely because barriers to entry prevent competitors from entering.
This persistent profit is the monopolist's reward — and the consumer's cost. It is a transfer from consumers (who pay higher prices) to the monopolist (who earns the profit). The deadweight loss is additional — it's value that nobody gets.
19.3 Price discrimination
A monopolist with market power has another option: instead of charging the same price to everyone, it can charge different prices to different customers. This is price discrimination — one of the most common and most interesting features of real monopolistic markets.
Three degrees of price discrimination
First-degree (perfect) price discrimination. The firm charges each customer exactly their willingness to pay. Every unit is sold at a different price. The monopolist captures all consumer surplus. There is no deadweight loss (every efficient trade happens). But the consumer gets nothing — all the surplus goes to the producer.
This is rare in practice (the firm would need to know every customer's willingness to pay). The closest real-world examples: car dealers (who negotiate individually with each buyer), some professional services (lawyers and consultants who charge different clients different rates), and some online retailers (which use browsing data to personalize prices).
Second-degree price discrimination. The firm charges different prices depending on the quantity purchased or the version of the product. Bulk discounts (buy 10 get one free), tiered pricing (basic/premium/enterprise software), and versioning (economy/business/first class on an airline) are all second-degree discrimination.
The economic logic: customers self-select into tiers based on their willingness to pay. The firm doesn't need to know each customer's willingness to pay; it just needs to design the menu so that high-willingness-to-pay customers choose the expensive tier and low-willingness customers choose the cheap tier.
Third-degree price discrimination. The firm charges different prices to different groups identified by observable characteristics: students, seniors, military, children, different geographic regions, different times of day.
Examples: - Movie theaters: $12 for adults, $8 for students, $6 for seniors - Airlines: different prices for the same seat depending on when you book, how flexible the ticket is, and whether you're traveling for business or leisure - Software: student versions at steep discounts; enterprise versions at premium prices - International pricing: the same product at different prices in different countries based on local willingness to pay
Third-degree discrimination is the most common form. It requires: (1) the firm has market power (a perfectly competitive firm can't price-discriminate — everyone faces the same market price), (2) the firm can identify the groups, and (3) the firm can prevent resale (students can't buy cheap tickets and resell them to adults).
Is price discrimination bad?
It depends. From a pure efficiency standpoint, price discrimination can increase efficiency compared to single-price monopoly. First-degree discrimination eliminates the deadweight loss entirely (all efficient trades happen). Third-degree discrimination that brings new customers into the market (students who wouldn't have attended at the full price) can increase total surplus.
But price discrimination also transfers surplus from consumers to the firm. And it can feel unfair — why should two people sitting in adjacent airplane seats pay vastly different prices for the same flight?
The honest economic framing: price discrimination is a tool that can be used well (expanding access to people who would otherwise be priced out) or badly (extracting maximum surplus from captive customers). The evaluation depends on the specific case.
19.4 The tech monopoly question
The most contested contemporary monopoly debate is about Big Tech: Google, Apple, Amazon, Meta (Facebook/Instagram/WhatsApp), and Microsoft.
The case that they ARE monopolies
Google has about 90% of the global search market. Bing and DuckDuckGo exist but have tiny shares. Google's dominance is sustained by network effects (more users → more data → better search → more users) and default agreements (Google pays Apple billions of dollars per year to be the default search engine on iPhones).
Amazon has about 38% of U.S. e-commerce — not a traditional monopoly share, but the platform's dominance of the online retail infrastructure (fulfillment, delivery, cloud services, third-party marketplace) gives it enormous power over both sellers and buyers.
Meta controls Facebook, Instagram, WhatsApp, and Threads — the dominant social networking platforms. Network effects make it very hard for competitors (Meta acquired Instagram and WhatsApp specifically to eliminate potential competitors).
Apple controls the iOS ecosystem and takes a 30% commission on all App Store transactions — a gatekeeper position that some argue constitutes monopoly power over app distribution.
Microsoft has about 75% of the desktop operating system market (Windows) and dominant positions in office productivity software and cloud computing.
Each of these firms has characteristics that resemble monopoly: dominant market share, barriers to entry (network effects, data advantages, ecosystem lock-in), and the ability to earn persistent economic profit.
The case that they are NOT monopolies (or not harmful ones)
The consumer welfare standard. Since the 1980s, U.S. antitrust law has been interpreted through the consumer welfare standard: a monopoly is harmful only if it raises prices or reduces output for consumers. By this standard, many tech firms are not harmful monopolies because their products are free (Google Search, Facebook, Instagram) or cheap (Amazon offers low prices). If the consumer isn't paying more, how can there be consumer harm?
Competition is one click away. Tech firms argue that their dominance is fragile because consumers can switch easily. Google dominates search, but a user can switch to Bing in seconds. Amazon dominates e-commerce, but a customer can buy from any website. The barrier to switching is lower than in traditional monopolies (you can't easily switch your water utility).
Innovation benefits. Tech firms invest heavily in R&D and have produced genuine innovations (search algorithms, cloud computing, social networking, smartphones). Antitrust action that reduced their market power might also reduce their incentive and ability to innovate.
Market definition matters. Google has 90% of search — but if you define the market as "online advertising" (which includes social media advertising, display advertising, and video advertising), Google's share is about 28%. Amazon has 38% of e-commerce — but if you define the market as "all retail," its share is about 6%. Whether a firm is a monopoly depends on how you define the market.
Where the debate stands
The debate is genuinely unsettled. Some changes are happening:
- The EU has been more aggressive than the U.S., imposing large fines on Google (for favoring its own products in search results) and passing the Digital Markets Act (which requires large platforms to allow interoperability and limits self-preferencing).
- The U.S. Department of Justice filed antitrust suits against Google (2020, for search dominance) and Apple (2024, for App Store practices). A federal judge ruled in 2024 that Google had maintained an illegal monopoly in search. The remedies are still being determined.
- The FTC filed suit against Meta (2020) and has challenged several tech acquisitions.
The honest economic assessment: Big Tech firms have market power that resembles monopoly in important ways (dominant share, barriers to entry, persistent profit). Whether this market power is harmful depends on how you measure harm — the consumer-welfare standard says prices are low, so there's no harm; a broader standard that considers data privacy, political influence, innovation competition, and platform power would reach a different conclusion.
The debate will not be settled in this textbook. What the textbook can give you is the framework for analyzing it: monopoly pricing, deadweight loss, barriers to entry, network effects, price discrimination, and the consumer-welfare standard. With these tools, you can evaluate the arguments for yourself.
19.5 Antitrust: what the government can do
The U.S. has two major antitrust laws:
The Sherman Act (1890): prohibits "monopolization" and "attempts to monopolize." It was used to break up Standard Oil (1911) and AT&T (1984).
The Clayton Act (1914): prohibits mergers and acquisitions that substantially lessen competition. It was used to block proposed mergers (AT&T/T-Mobile in 2011) and to challenge completed mergers (the FTC's challenge of Meta's acquisition of Within in 2022).
Antitrust remedies include: - Structural remedies: breaking up the monopolist (as with Standard Oil and AT&T) - Behavioral remedies: requiring the monopolist to change its practices (stop self-preferencing, open its platform, allow interoperability) - Blocking mergers: preventing the monopolist from acquiring competitors
The history of U.S. antitrust enforcement has two eras: - The activist era (1890s–1970s): aggressive enforcement, many breakups and merger challenges, broad interpretation of "competition" - The Chicago School era (1980s–2020s): the consumer-welfare standard narrowed enforcement to cases where prices were demonstrably raised or output reduced. Many mergers that earlier courts would have blocked were allowed. Tech monopolies grew largely unchallenged. - The emerging "neo-Brandeisian" era (2020s): a new generation of antitrust thinkers (led by Lina Khan at the FTC, Jonathan Kanter at the DOJ, and Tim Wu in academia) argues that the consumer-welfare standard is too narrow and that market power should be addressed even when prices are low. This view is gaining influence but has not yet reshaped the law.
19.6 Where this is going
Chapter 19 gave you the pure monopoly model. Chapter 20 will give you the two intermediate cases — monopolistic competition (many firms, differentiated products, free entry) and oligopoly (a few firms, strategic interaction). Chapter 21 will apply all of this to the labor market, where monopsony (monopoly on the buying side) complicates the standard competitive story and helps explain the minimum-wage debate.
Key terms recap: monopoly — one firm, no close substitutes, barriers to entry market power — the ability to set price above marginal cost barrier to entry — something that prevents competitors from entering natural monopoly — one firm can supply the market at lower cost than two network effect — value increases as more people use the product deadweight loss of monopoly — the surplus lost because the monopolist produces less than the competitive quantity price discrimination — charging different prices to different customers for the same product consumer welfare standard — antitrust harms judged by effect on consumer prices Sherman Act / Clayton Act — the two main U.S. antitrust laws
Themes touched: Markets power+imperfect (monopoly is the most dramatic imperfection), Tradeoffs (monopoly profit vs. deadweight loss; innovation incentive vs. consumer harm), Disagreement (about Big Tech and the right antitrust standard), Affects daily life (Google, Amazon, Apple, Meta, your drug prices).