What you'll learn
Perfect competition and monopoly are the extremes. Almost every market a Caribbean student actually encounters sits between them, and this topic covers that middle ground: monopolistic competition and oligopoly.
Monopolistic competition has many firms, free entry, and — the crucial difference from perfect competition — a differentiated product. Each hairdresser, restaurant or minibus operator offers something slightly distinct, so each faces a downward-sloping demand curve and has a little price-setting power. But because entry is free, supernormal profit is still competed away in the long run.
Oligopoly has a few large firms dominating the market, and its defining feature is interdependence: each firm's best action depends on what its rivals do. That single fact makes oligopoly the least predictable structure and the one where firms are most tempted to collude rather than compete.
By the end you should be able to describe each structure, explain why monopolistic competition produces excess capacity, analyse the kinked demand curve and price rigidity, distinguish collusive from non-collusive behaviour, and evaluate non-price competition.
Key terms and definitions
Product differentiation — making a product distinct from rivals' in the buyer's mind, whether through real differences or branding.
Monopolistic competition — many firms, differentiated products, free entry and exit.
Oligopoly — a market dominated by a few large firms, each aware that its actions provoke responses.
Concentration ratio — the share of market output held by the largest few firms; a common measure of how oligopolistic a market is.
Interdependence — the condition in which each firm's best decision depends on rivals' expected reactions.
Kinked demand curve — a model explaining price rigidity: rivals match price cuts but not price rises.
Collusion — firms agreeing, openly or tacitly, to restrict competition. A formal agreement between them is a cartel.
Price leadership — tacit coordination in which one firm sets a price and others follow, without any explicit agreement.
Non-price competition — competing through branding, advertising, quality, service or loyalty schemes rather than price.
Excess capacity — producing below the output at which average total cost is minimised.
Core concepts
Monopolistic competition: a little market power
Because the product is differentiated, a firm can raise its price slightly without losing every customer — some buyers prefer that particular restaurant or barber. So the demand curve slopes downward, though it is highly elastic, because close substitutes are readily available.
In the short run, a firm can earn supernormal profit if demand is strong. In the long run, free entry means new firms enter, each taking a share of demand, so every firm's demand curve shifts left until only normal profit remains.
That long-run outcome shares one feature with perfect competition — normal profit only — and differs in an important respect.
The excess capacity result
In long-run equilibrium the monopolistically competitive firm produces where its downward-sloping demand curve is tangent to average total cost. Because the demand curve slopes down, that tangency occurs on the falling part of the average cost curve, not at its minimum.
So the firm produces less than the output that would minimise average cost, and it charges a price above marginal cost. It is therefore neither productively nor allocatively efficient, and the gap between actual output and minimum-cost output is called excess capacity.
The practical reading matters for evaluation: a town with eight small restaurants each half full is the excess capacity result in real life. Society pays higher average costs for the variety it gets. Whether that is a bad outcome is a judgement — consumers may value the choice highly, and an answer that weighs variety against cost is far stronger than one that simply labels the structure inefficient.
Oligopoly and interdependence
With only a few firms, each one's pricing and output decisions visibly affect the others, and each must anticipate their reactions. There is therefore no single determinate outcome the way there is in the other structures, which is why oligopoly is modelled several different ways.
Concentration ratios measure the degree of dominance — the combined share of the largest three or four firms. Caribbean markets in banking, cement, beverages and telecommunications are frequently highly concentrated, simply because the market is too small to support many firms at efficient scale.
The kinked demand curve and price rigidity
This model explains why oligopoly prices often stay unchanged for long periods even when costs move.
Assume each firm believes that if it cuts its price, rivals will match the cut to protect their share, so it gains very little extra demand — demand is inelastic below the current price. If it raises its price, rivals will hold theirs and take its customers, so it loses a great deal — demand is elastic above the current price.
The demand curve is therefore kinked at the existing price, and the marginal revenue curve has a gap at that output. Marginal cost can shift within that gap without changing the profit-maximising price at all. Prices stay rigid.
The model has a genuine weakness worth stating: it explains why a price, once established, tends to stay put, but it does not explain how that price came to be set in the first place.
Collusion and its instability
Because competition erodes profit, oligopolists have a strong incentive to collude — to agree on prices or market shares and behave collectively like a monopolist. A formal agreement is a cartel; an informal understanding, such as everyone following one firm's price announcements, is tacit collusion or price leadership.
Collusion is unstable for a reason worth understanding rather than memorising: once a high price is agreed, each member can gain by quietly undercutting it and capturing extra sales while the others hold the line. The incentive to cheat is strongest precisely when the agreement is working. Cartels therefore tend to break down unless they can monitor and punish defection.
Collusion is illegal in most jurisdictions because it reproduces monopoly outcomes — higher prices, restricted output — without even the scale advantages a genuine single firm might deliver.
Non-price competition
Where price competition is dangerous, because it invites matching and destroys everyone's margins, firms compete in other ways: advertising and branding, product quality and design, after-sales service, loyalty schemes, packaging and location.
This is why oligopolistic markets are the most heavily advertised. Evaluating it requires both sides: advertising informs buyers and funds broadcasting, but it also raises costs that consumers ultimately pay and can itself become a barrier to entry, since a new firm must match the incumbents' spending to be noticed.
Worked examples
Example 1 — Classifying a market (5 marks)
A town has twelve hairdressing salons. Each has its own regular customers, prices differ modestly, anyone can open a new salon, and no salon is large enough to influence the others.
Structure: monopolistic competition. Many firms, differentiated services, free entry, and a downward-sloping but highly elastic demand curve for each salon.
Prediction: in the long run, entry competes away supernormal profit and each salon earns normal profit only, operating with excess capacity — that is, below the output at which its average cost would be lowest.
Note what makes this monopolistic competition rather than perfect competition: the product is differentiated by location, skill and personal relationship, so customers do not treat every salon as identical.
Example 2 — The kinked demand curve (6 marks)
Three firms supply bottled gas in a territory, all charging $80 per cylinder.
If one cuts to $75, the others match immediately to protect their shares. The firm gains almost no extra customers, so demand below $80 is inelastic and the price cut simply reduces revenue.
If it raises to $85, the others hold at $80 and take its customers. Demand above $80 is elastic and the firm loses heavily.
Both moves are unattractive, so the firm keeps its price at $80. The demand curve is kinked at that price and the marginal revenue curve has a gap directly below the kink — so even a moderate rise in the cost of gas leaves the profit-maximising price unchanged.
The prediction is price rigidity, which matches what is often observed in such markets. The model's limitation is that it explains why $80 persists but not why $80 was chosen.
Example 3 — Why a cartel breaks down (5 marks)
Four cement producers agree to hold the price at $40 per bag and each supply a quarter of the market.
At $40 each earns substantial profit. But any one producer can quietly offer $37 to a large customer, win extra volume, and earn more than its agreed share while the others keep prices high.
Every member faces that same incentive, and each knows the others face it too. Unless the cartel can detect undercutting and punish it, suspicion alone tends to break the agreement.
The point for an answer: the incentive to cheat is strongest when the agreement is working best, because that is when the gap between the agreed price and a member's own marginal cost is widest.
Example 4 — Evaluating non-price competition (5 marks)
Two mobile network operators compete heavily on advertising, handset offers and loyalty points rather than on call prices.
For consumers: more information about what is available, service improvements, and bundled benefits that have real value.
Against: advertising is a cost recovered in prices; the spending may cancel out, so neither firm gains share and buyers fund an arms race; and heavy advertising raises the cost of entering, protecting the incumbents.
Conclusion: non-price competition is preferable to no competition at all, but it is a weaker substitute for price competition, because it raises costs while price competition lowers them. Where a regulator can act, encouraging price transparency is more valuable than restricting advertising.
Common mistakes and how to avoid them
Saying monopolistically competitive firms earn supernormal profit in the long run. Free entry competes it away, exactly as in perfect competition.
Confusing monopolistic competition with monopoly. Monopolistic competition has many firms and free entry; only the product differentiation is shared with monopoly.
Saying the kinked demand curve explains how the price is set. It explains why an existing price is rigid, not how it arose.
Treating excess capacity as deliberate waste. It is the consequence of producing a differentiated product on a downward-sloping demand curve.
Assuming all oligopolists collude. Some compete fiercely; interdependence permits either outcome.
Forgetting why cartels break down. The incentive to undercut is strongest when the agreement is most profitable.
Treating advertising as purely wasteful. It informs buyers and can support quality — evaluate both sides.
How this links to your Internal Assessment
Imperfect competition is the most realistic market structure for a Caribbean Internal Assessment, because genuine examples are everywhere: minibus routes, small restaurants, hardware shops, mobile networks, cement and beverages.
Classify the market with evidence. Count the firms, estimate the largest firms' combined share if you can, ask what a new entrant would have to overcome, and establish whether the product is differentiated. Those four pieces of evidence justify a classification rather than asserting one.
Then look for the predictions. Does the monopolistically competitive market show excess capacity — premises standing half empty, vehicles running below capacity? Does the oligopoly show rigid prices that stay unchanged while costs move? Evidence for or against a model's prediction is the most interesting finding your assessment can produce, and evidence against is worth just as much, provided you say what it implies.
Be careful about collusion. Suggesting that firms have agreed prices is a serious allegation. Report observed price similarity as an observation consistent with several explanations — including price leadership, similar costs, or genuine competition — rather than as proof of an agreement.
Exam technique for imperfect competition
Comparison questions are common, so answer on consistent criteria: number of firms, product differentiation, barriers to entry, the demand curve faced, long-run profit and efficiency. Working through the same list for each structure produces a well-organised answer almost automatically.
For the kinked demand curve, describe both halves separately — inelastic below the kink because rivals match cuts, elastic above it because they do not match rises — and then state the conclusion about rigidity. Marks are awarded for the reasoning, not just for the conclusion.
Command words are consistent. Describe the features of oligopoly wants the characteristics. Explain price rigidity wants the kinked demand reasoning. Analyse why a cartel is unstable wants the incentive to cheat set out. Evaluate non-price competition wants both sides and a stated conclusion.
Where a question names a local market, use it throughout. Small Caribbean economies concentrate naturally, and saying why — the market is too small for many firms at efficient scale — shows the understanding examiners reward.
Quick revision summary
- Monopolistic competition: many firms, differentiated products, free entry, highly elastic downward-sloping demand.
- Short run: supernormal profit possible. Long run: entry competes it away to normal profit.
- Excess capacity: the long-run tangency occurs on the falling part of average cost, so output is below minimum-cost output and price exceeds marginal cost.
- Society pays higher average cost for variety — whether that is worth it is a judgement, not a given.
- Oligopoly: a few dominant firms, defined by interdependence; concentration ratios measure it.
- Kinked demand: rivals match cuts but not rises, so demand is inelastic below and elastic above the current price.
- The gap in marginal revenue means costs can move without changing the profit-maximising price — hence rigidity.
- The kinked model explains why a price persists, not how it was set.
- Collusion reproduces monopoly outcomes; a formal agreement is a cartel, an informal one is tacit collusion or price leadership.
- Cartels are unstable because the incentive to undercut is greatest when the agreement is working best.
- Non-price competition dominates where price cuts would simply be matched; evaluate its information value against its cost and entry-barrier effect.