Monopolistic Competition & Contestability

Differentiation, excess capacity, the long-run adjustment, and why the threat of entry matters more than market structure

SPEC 3.4 • MARKET STRUCTURES

Key Definitions

Monopolistic Competition

A market structure with many firms selling differentiated products with low barriers to entry and exit.

Contestable Market

A market where the threat of potential competition is sufficient to keep prices competitive, even if few firms currently operate. Key condition: low sunk costs and freedom of entry/exit.

Sunk Costs

Costs that cannot be recovered if a firm exits a market (e.g. advertising, specialist equipment, brand investment).

Characteristics of Monopolistic Competition

Monopolistic competition sits between perfect competition and oligopoly on the market structure spectrum. Think: hairdressers, restaurants, independent coffee shops, clothing retailers.

Four Characteristics

Many firms — large number of sellers, each with a small market share

Differentiated products — each firm's product is slightly different (brand, quality, location, service)

Low barriers to entry and exit — fairly free entry; some sunk costs but not prohibitive

Some price-making power — differentiation gives a slightly downward-sloping demand curve, but limited ability to raise prices far above rivals

Exam Tip

In a "identify the market structure" question (e.g. Nov 2021 P3 Q1 — car washes), list multiple characteristics with context: many firms + low capital + differentiated service + low profit margins. Each characteristic with applied context = 2 marks.

Short Run — Supernormal Profit

In the short run, a monopolistically competitive firm can earn supernormal profit through its differentiation advantage. The diagram looks similar to monopoly — downward-sloping AR, MR below it, profit max at MC = MR.

Key Point

This supernormal profit is temporary. Because barriers to entry are low, new firms will be attracted into the market. This triggers the long-run adjustment.

The Long-Run Adjustment

New firms enter with their own differentiated products. Demand for existing firms falls — the AR curve shifts left — until normal profit is reached.

SR supernormal profit

Low barriers → new firms enter

Demand for existing firms falls

AR shifts left

AR tangent to ATC

Normal profit only

Excess Capacity — The Key Concept

In long-run equilibrium, the AR curve is tangent to ATC — but not at its minimum point. The firm operates on the downward-sloping portion of the ATC curve, to the left of minimum efficient scale.

Why Excess Capacity Matters

The firm produces at Q* < Qe (where Qe = min ATC output)

This means the firm is not productively efficient — it could lower average cost by producing more

But it cannot produce more because demand is limited by differentiation — it would have to lower price below ATC

This is the fundamental trade-off of monopolistic competition: product variety at the cost of some productive inefficiency

Examiner Alert

A common error is saying monopolistic competition achieves productive efficiency in the long run because it earns normal profit. Normal profit ≠ productive efficiency. Productive efficiency requires P = min ATC. In monopolistic competition, the tangency point is above min ATC.

Monopolistic Competition vs Perfect Competition

This comparison is a favourite exam question. Both structures share some features but differ crucially in efficiency outcomes.

FeaturePerfect CompetitionMonopolistic Competition

Number of firmsManyMany

ProductsHomogeneousDifferentiated

Barriers to entryNoneLow (some sunk costs)

Demand curvePerfectly elastic (horizontal)Slightly downward sloping

LR profitNormal profitNormal profit

Allocative efficiency✓ (P = MC)✗ (P > MC)

Productive efficiency✓ (P = min ATC)✗ (excess capacity)

Product varietyNoneYes — consumer choice

Exam Tip

Similarity: Both reach normal profit in LR due to free entry. Key difference: Monopolistic competition has excess capacity. Evaluation: The efficiency loss may be worth the consumer benefit of product variety.

Non-Price Competition

Because monopolistically competitive firms sell differentiated products, they compete primarily through non-price methods rather than pure price cuts.

Forms of Non-Price Competition

Product quality — improving the product itself (speed, reliability, ingredients)

Branding & advertising — creating perceived differences even where products are similar

Customer service — after-sales support, loyalty schemes, personalisation

Location & convenience — being closer or more accessible than rivals

Innovation — new features, menu items, service styles

Non-price competition is how firms maintain their downward-sloping demand curve. Without differentiation, the demand curve would become horizontal and the firm would become a price taker — effectively perfect competition.

Real-World Application — Car Washes (Nov 2021 P3)

10,000–20,000 firms, low capital required, ~£5 price. Differentiation: inside/outside washes, speed, location, hand vs machine wash. Low profit margins indicate easy entry — consistent with monopolistic competition.

From Structure to Behaviour — Contestability

So far, we've analysed markets by their structure — how many firms, what barriers exist. Contestability theory asks a different question: does the structure actually determine behaviour?

The Key Insight

It is the threat of entry, not actual entry, that disciplines firms. A market with only two firms could be highly competitive if it is contestable. A market with ten firms could be collusive if it is not.

Low sunk costs

Easy entry & exit

Threat of hit-and-run entry

Incumbent prices near competitive level

Normal profit even with few firms

Exam Tip

Contestability is one of the most powerful AO4 evaluation points on the entire course. Use it in ANY market structure essay to challenge the assumption that concentration = exploitation.

Contestable Markets — Key Features

Conditions for a Perfectly Contestable Market

No sunk costs — all costs are recoverable on exit

Freedom of entry and exit — no legal or strategic barriers

Access to same technology — entrants face same cost curves as incumbents

Perfect information — entrants know incumbents' prices and profits

Hit-and-Run Entry

Potential competitors can enter quickly, undercut prices, earn profit, and exit before incumbents can respond — possible only if sunk costs are low.

In a perfectly contestable market, even a monopolist earns only normal profit — because any supernormal profit would attract hit-and-run entrants who undercut the price.

Limit Pricing & Strategic Deterrence

If a market is contestable, incumbents may use strategic pricing to deter entry — even before any entrant appears.

Limit Pricing

Setting price just low enough to deter new entrants — the entrant cannot cover costs at the limit price, so does not enter. The incumbent sacrifices some short-run profit to maintain long-run market position.

Strategies to Reduce Contestability

Predatory pricing — pricing below cost to force rivals out (illegal if abusing dominance)

Limit pricing — pricing just above cost to deter entry

Heavy advertising — raises sunk costs for entrants

Brand loyalty — makes demand for entrants' products less elastic

Excess capacity — signals ability to flood market if entrant arrives

Strategies to Increase Contestability

Deregulation — removing legal barriers (e.g. airline routes)

Competition policy — CMA preventing anti-competitive mergers

Technology — lowers set-up costs (e.g. online retail)

Open access to infrastructure — e.g. rail track access for new operators

Contestability in Practice

Airlines are the classic exam example — but the theory applies across many industries.

MarketContestabilityWhy?

Airline routesHigh (where low-cost carriers can enter)Planes can be redeployed to other routes; low sunk costs on competitive routes

Online retailHighLow set-up costs, no physical premises needed, platform access

HairdressingHighLow capital, portable skills, minimal sunk costs

Water supplyVery lowMassive infrastructure sunk costs, natural monopoly

Social mediaLowNetwork effects create huge sunk costs; users don't switch easily

BankingLow–MediumRegulatory barriers high, but fintech lowering entry costs

The Airline Insight

Routes with no credible low-cost alternative have high fares. Routes where low-cost carriers could easily enter have competitive fares. The incumbent must price as if it were competitive — or invite competition.

Efficiency Summary

Efficiency TypeMonopolistic CompetitionContestable Market (with few firms)

Allocative (P = MC)✗ — P > MC (downward-sloping AR)Approaches ✓ — threat of entry forces P toward MC

Productive (min ATC)✗ — excess capacity in LRApproaches ✓ — cost minimisation to deter entry

Dynamic (R&D)Limited — normal profit constrains R&DDepends — threat of entry may incentivise innovation

X-inefficiencyLow — competitive pressure from many rivalsLow — threat of entry eliminates slack

Examiner Alert

Do NOT say contestable markets are always allocatively efficient. They approach competitive outcomes — the extent depends on how low sunk costs actually are. "Perfectly contestable" is a theoretical benchmark, like "perfectly competitive."

AO4 Evaluation Toolkit

Evaluative ArgumentDevelopment

Product variety trade-offExcess capacity is the cost of differentiation. Consumers benefit from choice — the efficiency loss may be worth the variety gain.

Contestability challenges structureA concentrated market with low sunk costs may behave competitively. Structure alone doesn't determine behaviour.

Sunk costs in practiceFew markets are perfectly contestable. Advertising, brand investment, and specialist equipment create sunk costs that limit the threat of entry.

Technology reduces barriersDigital platforms (Uber, Deliveroo, Etsy) lower entry costs in traditionally non-contestable markets → increased competition over time.

Incumbents can deter entryLimit pricing, predatory pricing, excess capacity all reduce contestability. CMA intervention may be needed to maintain competitive threat.

Common Errors — From Examiner Reports

Examiner Alert — Monopolistic Competition

Confusing normal profit with productive efficiency — normal profit means AR = ATC, NOT P = min ATC

Drawing the LR diagram with AR tangent at min ATC — the tangent is on the downward-sloping portion, to the LEFT of minimum ATC

Forgetting to show AR shifting left in the SR → LR adjustment — new entry causes demand for individual firms to fall

Saying "no barriers to entry" — monopolistic competition has LOW barriers, not zero (some sunk costs exist)

Examiner Alert — Contestability

Claiming all markets are contestable — most markets have some sunk costs; perfectly contestable is a theoretical extreme

Confusing contestability with competition — contestability is about the THREAT of entry, not the number of firms currently in the market

Not defining sunk costs — always define: costs that cannot be recovered if a firm exits

Practice Question

Question (15 marks): Evaluate whether monopolistic competition leads to an efficient allocation of resources.

Use diagrams to support your answer. Consider both short-run and long-run outcomes.

1

Define monopolistic competition (many firms, differentiated products, low barriers) and allocative efficiency (P = MC).

2

KAA 1 — Inefficiency: In LR, AR tangent to ATC (normal profit) but NOT at min ATC → productive inefficiency (excess capacity). P > MC → allocative inefficiency. Draw LR diagram with AR tangent above min ATC. "As shown in the diagram, Q* is to the left of minimum efficient scale Qe."

3

KAA 2 — The benefits: Differentiation delivers product variety and consumer choice. Non-price competition incentivises quality improvement. Compared to monopoly, low barriers mean no sustained supernormal profit — consumers are not exploited.

4

Evaluation: (i) The efficiency loss (excess capacity) may be small if the market is highly contestable — the threat of entry keeps firms near competitive pricing. (ii) Product variety has real value to consumers — comparing to perfect competition ignores that consumers may prefer choice over minimal cost. (iii) The extent of inefficiency depends on how differentiated products actually are — if differentiation is mostly perceived (branding) rather than real, the efficiency cost may not be justified.

5

Conclusion: "Monopolistic competition does not achieve an efficient allocation by the strict criteria of P = MC and P = min ATC. However, the productive inefficiency is modest and is the price consumers pay for variety and choice. Whether this is 'inefficient' depends on whether we value static efficiency or consumer welfare more broadly."

Summary

Key Facts

ConceptDetail

Monopolistic competitionMany firms, differentiated products, low barriers, some price-making power

SR outcomeSupernormal profit possible (like monopoly)

LR outcomeNormal profit — AR tangent to ATC (NOT at min ATC)

Excess capacityFirm produces Q* < Qe → not productively efficient

Contestable marketThreat of entry disciplines pricing — key condition: low sunk costs

Hit-and-run entryPossible only if sunk costs ≈ 0

MC vs PC — Similarities

Many firms

Low barriers

Normal profit in LR

MC vs PC — Differences

Differentiated (not homogeneous)

Downward-sloping AR (not horizontal)

Excess capacity in LR

P > MC (allocatively inefficient)

The Golden Rule

Contestability is the most powerful AO4 evaluation point for ANY market structure question. Always ask: "How contestable is this market?" If sunk costs are low, the static analysis of monopoly power overstates the harm to consumers.