Unit 3: Market Structures

I. Orientation

Market structure describes the competitive environment in which firms and consumers make decisions. It is determined by the number and size of firms, the nature of the product, barriers to entry and exit, and the degree of control firms have over price. The central economic principle is that a profit-maximising firm produces where marginal revenue equals marginal cost, subject to its demand conditions.

• Market classification: The main structures are perfect competition, monopoly, monopolistic competition and oligopoly.
• Revenue concepts: Total revenue is (TR=P\times Q); average revenue is (AR=TR/Q); marginal revenue is (MR=\Delta TR/\Delta Q).
• Cost concepts: Total cost includes fixed and variable costs; marginal cost is the additional cost of producing one more unit.
• Profit rule: A firm maximises profit where (MR=MC), provided marginal cost is rising at the output chosen.
• Short run and long run: Fixed factors may exist in the short run, while all factors can be varied in the long run.
• Efficiency benchmark: Allocative efficiency occurs when (P=MC), while productive efficiency occurs at the minimum point of average cost.

II. Perfect Competition — Price-taking and market efficiency

Perfect competition is an idealised market structure in which many small firms sell an identical product and no individual firm can influence the market price.

A. Meaning and features

Perfect competition means that market demand and supply determine price, while each individual firm accepts that price as given.

• Large number of buyers and sellers: Each firm supplies an insignificant share of total output; therefore, losing one firm does not materially alter market supply.
• Homogeneous product: Wheat of a standard grade is an example; buyers treat one seller’s product as identical to another’s.
• Free entry and exit: Firms can enter when profits are available and leave when losses persist, assuming no legal, financial or technological barriers.
• Perfect knowledge: Buyers know prevailing prices and firms know relevant market and production conditions.
• Perfect mobility of factors: Labour and capital can move between uses, allowing resources to respond to changes in returns.
• Price-taking behaviour: A firm faces a perfectly elastic demand curve at the market price, so its average revenue and marginal revenue are equal to price.

B. Price and output determination of the firm and industry under perfect competition

Under perfect competition, the industry determines price through market demand and supply, while the firm chooses output where its (MC) curve intersects the fixed price line.

• Industry equilibrium: Market equilibrium occurs where industry demand equals industry supply. The resulting equilibrium price is (P_e), and total industry output is (Q_e).
• Firm demand curve: At (P_e), the individual firm can sell any feasible quantity at the market price but cannot charge more because buyers would switch immediately.
• Revenue relationship: Since (P=AR=MR), the firm’s profit condition is:

Profit maximisation: MR = MC
For a competitive firm: P = MR = MC

Here, (P) is price, (MR) is marginal revenue and (MC) is marginal cost.

• Short-run profit: If (P>ATC) at the equilibrium output, the firm earns abnormal or economic profit. (ATC) means average total cost.
• Normal profit: If (P=ATC), the firm earns only normal profit, which is the minimum return needed to keep resources in their present use.
• Short-run loss: If (AVC<P<ATC), the firm continues operating because price covers average variable cost and contributes something toward fixed cost. (AVC) means average variable cost.
• Shutdown point: If (P<AVC), the firm shuts down in the short run because producing would not cover variable costs.
• Long-run adjustment: Economic profit attracts entry, increasing industry supply and reducing price. Losses cause exit, decreasing supply and raising price until firms earn normal profit.
• Efficiency: In long-run equilibrium, (P=MC=minimum\ ATC), showing both allocative and productive efficiency under the model.

III. Monopoly — A single dominant supplier

A monopoly exists when one firm supplies a product or service for which close substitutes are unavailable and entry by competing firms is strongly restricted.

A. Meaning and features

Monopoly is a market structure in which the industry consists of one firm, so the firm and the industry are effectively the same entity.

• Single seller: A national electricity distributor with exclusive control over a transmission network may be the only supplier in a geographical area.
• No close substitutes: Consumers cannot easily replace the product; this makes the demand for the monopolist’s product relatively inelastic.
• High barriers to entry: Barriers may be legal, technological, financial or strategic.
  • Legal barriers: Patents, licences and government franchises can exclude competitors.
  • Natural barriers: Large economies of scale may make one supplier cheaper than several suppliers, creating a natural monopoly.
• Price-making power: The monopolist does not accept a market price; it selects a price-output combination along the downward-sloping market demand curve.
• Downward-sloping demand: To sell more units, the monopolist generally must reduce price, so (MR<P) for output above the first unit.
• Possibility of long-run abnormal profit: Entry restrictions allow economic profit to persist even in the long run.

B. Price and output determination under monopoly

A monopolist maximises profit by choosing output where marginal revenue equals marginal cost and then charging the highest price consumers will pay for that output on the demand curve.

• Equilibrium output: The profit-maximising output (Q_m) satisfies:

MR(Q_m) = MC(Q_m)
Price = Demand curve at Q_m

Here, (Q_m) is monopoly output, (MR) is marginal revenue and (MC) is marginal cost.

• Price determination: After identifying (Q_m), the firm moves vertically to the demand or average revenue curve to find monopoly price (P_m). It does not use the (MR) curve to read price.
• Profit measurement: Economic profit equals ((P_m-ATC_m)\times Q_m), where (ATC_m) is average total cost at monopoly output.
• Loss minimisation: If the monopolist cannot cover average total cost but can cover average variable cost, it may continue in the short run. It shuts down when (P<AVC).
• No unique supply curve: A monopoly has no supply curve independent of demand because its chosen output depends simultaneously on demand, marginal revenue and marginal cost.
• Allocative inefficiency: Monopoly generally produces where (P>MC), meaning consumers’ marginal valuation exceeds the cost of the last unit produced.
• Deadweight loss: Output below the competitive level prevents mutually beneficial transactions and creates a welfare loss.
• Price discrimination: If resale can be prevented and consumer groups differ in willingness to pay, the monopolist may charge different prices. A common condition is that groups with more inelastic demand face higher prices.

IV. Monopolistic Competition — Differentiated products and rivalry

Monopolistic competition combines many competing firms with product differentiation. Firms possess limited price-setting power, but entry and close substitutes restrict long-run profit.

A. Meaning and features

Monopolistic competition is a market structure in which many firms sell similar but not identical products and compete through both price and non-price methods.

• Many firms: Each firm is small relative to the industry, but its individual brand has some separate demand.
• Product differentiation: Differences may involve quality, design, location, packaging, service, advertising or brand image. Restaurants and clothing brands commonly illustrate this feature.
• Close substitutes: Because alternatives exist, a firm’s demand is more elastic than a monopolist’s demand.
• Free or relatively easy entry and exit: New firms can enter when existing firms earn economic profit, although start-up costs and brand loyalty may delay entry.
• Downward-sloping demand curve: A firm can raise price without losing every customer because some buyers prefer its differentiated product.
• Non-price competition: Advertising, customer service, warranties and product innovation may shift or alter the firm’s demand.
• Excess capacity: Firms may operate below the output that minimises average total cost because each firm faces a downward-sloping demand curve.

B. Price and output determination under monopolistic competition

A monopolistically competitive firm chooses output at (MR=MC), then charges the price shown on its product-specific demand curve.

• Short-run equilibrium: The firm behaves like a small monopolist for its brand:
  • It faces a downward-sloping demand curve.
  • Its (MR) curve lies below demand.
  • It selects output where (MR=MC).
• Price and profit: The price is read from the demand curve at the chosen quantity. If (P>ATC), the firm earns abnormal profit; if (P<ATC), it makes a loss.
• Long-run entry: Abnormal profit attracts new firms offering similar products. Customers are distributed across more brands, shifting each existing firm’s demand curve leftward and making it more elastic.
• Long-run exit: Persistent losses cause some firms to leave, increasing the demand available to remaining firms.
• Long-run equilibrium: Entry and exit continue until the firm earns normal profit, generally where the demand curve is tangent to the (ATC) curve:

Long-run condition: MR = MC
                         and
                    P = ATC

Here, (P) is the firm’s price, (ATC) is average total cost, (MR) is marginal revenue and (MC) is marginal cost.

• Economic inefficiency: Because the firm usually produces where (P>MC), output is below the allocatively efficient level.
• Productive inefficiency: Tangency occurs on the declining portion of (ATC), so the firm operates with excess capacity rather than at minimum average cost.
• Consumer benefit: Although efficiency is sacrificed, consumers gain variety, branding and differentiated product characteristics.

V. Oligopoly — Strategic interdependence among a few firms

Oligopoly is a market structure dominated by a small number of large firms whose decisions are mutually dependent.

A. Meaning and features

Oligopoly exists when a few firms account for a substantial share of industry sales and each firm must anticipate how rivals will respond to its actions.

• Few dominant firms: The industry may contain two firms, called a duopoly, or several large firms such as major automobile producers.
• Mutual interdependence: A price cut by one firm may trigger matching cuts by rivals, while a price increase may cause customers to switch to competitors.
• Significant barriers to entry: Economies of scale, high capital requirements, patents, control over distribution and strong brand loyalty can protect existing firms.
• Product type: Products may be homogeneous, as in some raw-material markets, or differentiated, as in automobiles and smartphones.
• Strategic behaviour: Firms consider competitors’ likely reactions before changing price, output, advertising or investment.
• Non-price competition: Advertising, research, product design and service may be preferred to price cuts because direct price competition can reduce every firm’s revenue.
• Price rigidity: In the kinked-demand explanation, a firm expects rivals to follow a price reduction but not a price increase, making the demand curve kinked and price relatively stable.
• Collusion and cartels: Firms may coordinate output or prices to raise joint profit, but such agreements are often illegal and unstable because each member has an incentive to secretly expand sales.
• No single general model: Outcomes range from intense competition to collusive monopoly-like behaviour, depending on information, enforcement, costs and strategic expectations.
• Uncertainty of equilibrium: Unlike perfect competition or simple monopoly, oligopoly does not have one universally applicable price-output rule; game theory is often used to analyse the strategic choices of firms.