Monopoly and Contestability
~40 min · WEC13 · 3.3.3
WEC13 · 3.3.3 · 40 min
A with one firm and a market that's genuinely can look identical from the outside — yet the mark scheme reaches opposite verdicts on how that firm actually behaves, purely from whether entry is a credible threat.
Key terms in this lesson
Before you read on
Two or three questions on exactly what this lesson teaches. Being wrong here is fine — it's the fastest way to find out what to pay attention to next.
Monopoly: the sharpest market-structure assumption, and its guaranteed inefficiency
A is the sharpest possible market-structure assumption: a single dominant seller facing no close substitute, protected by high enough to keep it that way. Because there's no second firm sharing demand with it, the monopolist's own demand curve IS the market demand curve — AR=D, not a stylised individual-firm slice like perfect and monopolistic competition give each firm. The barrier types themselves are the same six sources Oligopoly names (spec 3.3.3.5b: economies of scale, limit pricing, patents, branding, sunk costs, legal restriction) — what's specific to monopoly (spec 3.3.3.6b) is that they have to be close to complete, not just high: an oligopoly's barriers keep the number of firms small; a monopoly's barriers keep it at exactly one, indefinitely — which is exactly why monopoly profit can stay supernormal into the long run in a way perfect and monopolistic competition's can't.
Profit-maximising equilibrium (spec 3.3.3.6c) works by the same rule as every other market structure this course has covered — MR=MC — but AR=D being the whole market changes the verdict completely. A price-taking firm has P=MR=MC built in; a monopolist's MR sits below its AR at every output, so MR=MC settles where P is strictly above MC. Allocative inefficiency isn't a possible outcome for a monopolist, it's the guaranteed one, short run and long run alike, because there's no free-entry mechanism to compete supernormal profit away. Pearson's own verified example makes this link explicit: on a real Oct 2021 essay about MTN Ghana, the mark scheme states directly, "Monopolies will not be allocatively efficient as the lack of competition, such as MTN Ghana controlling 70% of the market, allows them to charge higher prices (P>MC) than in a more competitive industry." The benefit case isn't nothing, and a Level 3+ evaluation has to engage it, not just gesture at it: a monopolist shielded from competitive pressure can capture the same the Economies of Scale lesson derived, potentially passing some of the resulting lower average cost through to consumers; and supernormal profit is exactly the kind of retained resource that funds investment — R&D, new products — that a firm earning only normal profit in a competitive market can't as easily afford. The same supernormal profit also lets a monopolist cross-subsidise a loss-making part of its business using profit earned elsewhere — the real mark scheme credits this directly as a genuine increase in consumer choice, not merely an internal accounting convenience, since it can keep a product line running that a firm earning only normal profit couldn't afford to sustain at a loss (verified: "A monopolist may be able to cross subsidise loss-making parts of its business and cover the losses with the supernormal profits made in other parts of the business. This increases consumer choice."). Where a monopoly supplies something essential, like water or energy, governments typically regulate rather than break it up — price ceilings forcing P=MC, profit caps, quality standards — though a real, verified mark-scheme point cuts the other way too: "if regulatory capture occurs the regulator may become focused on the interests of the firms they regulate rather than on the public interest." The Government Intervention lesson develops this regulatory toolkit in full; this lesson only needs the aside.
Spec 3.3.3.6h asks for all three efficiency verdicts on a monopoly, not just the allocative one just derived — and the same real Oct 2021 mark scheme credits productive inefficiency and X-inefficiency as genuinely separate, separately-markable points, not restatements of P>MC in different words; the examiner report on this exact question confirms the distinction matters, describing the stronger responses' diagrams as "well linked... to both allocative and productive inefficiency." Productive inefficiency: verified verbatim, "a monopoly may be productively inefficient if it restricts output below the lowest point on the AC curve" — on the diagram below, Qm sits well to the left of the output where AC bottoms out (where MC crosses AC), so the monopolist is producing at a higher unit cost than its own technology would allow at a larger scale, a second and distinct inefficiency from the P>MC allocative result above, not the same claim restated. X-inefficiency: the same mark scheme states the mechanism directly rather than just naming it — "the lack of competition and inelastic demand enables the business to increase the price without a proportionate fall in quantity demanded. If costs increase the monopoly can allow prices to increase to cover the rising costs" — weak competitive pressure lets a monopolist's own average costs drift upward and simply pass the rise on to price, rather than needing to control it the way a competitive firm, facing far more elastic demand for its own individual output, would be forced to. The consumer-side harm isn't only a pricing story either: the same mark scheme separately credits product-quality decline as its own channel, verified verbatim — "MTN Ghana can abuse their dominant position by offering low quality products to consumers to save on costs of production. As consumers have limited other options but to purchase from them, consumer welfare decreases" — a monopolist facing no substitute has nothing forcing it to compete on quality either, a genuinely different harm from the price-and-output story the diagram measures.
(spec 3.3.3.6e) is a specific cost-structure claim, not just "a monopoly that occurs naturally": it's a market where long-run average cost keeps falling across the entire range of output the market could realistically demand, so one firm supplying everyone is genuinely cheaper than splitting that same demand between two or more competing firms, each stuck on a higher point of the same falling LRAC curve. Utility networks — water pipes, electricity grids, rail track — are the standard case, because duplicating the physical network itself is the wasteful part, not the service running over it. Pearson's own verified evaluative aside states the logic directly: "If the monopoly is a natural monopoly it is more efficient to have a single seller in the market achieving economies of scale, than to have firms competing."
Why a train company charges commuters more than leisure travellers, before the three conditions
In plain terms
A train company sells the 8am seat on one route to two different kinds of passenger. Commuters have to be at their desk by 9 and have no real alternative to this exact train — barely responsive to price, i.e. inelastic demand. Leisure travellers could just as easily go a different day, take the coach, or drive instead — highly responsive to price, i.e. elastic demand. It costs the company $10 to carry one more passenger either way (staff time, cleaning, ticket processing) — the marginal cost, the same for both groups. Take commuters on their own first. At $48 a seat, 1 buys. Selling a 2nd needs the price down to $46 — for BOTH commuters, since everyone in the group pays whatever the current price is — so revenue goes $48 to $92, a gain of $44 from that 2nd seat. Keep going and the gain from each extra seat keeps shrinking, same reason as always: cutting price to sell one more also cuts it on everyone already committed to buying. By the 10th commuter seat, price has fallen to $30, revenue is $300, and that 10th seat still gained $12 — more than the $10 it costs to carry them, so sell it. An 11th would need $28 and only gain $8 — less than $10, so stop at 10. Commuters, profit-maximising: 10 seats at $30 = $300. Leisure travellers need much bigger price cuts to shift the same number of seats, since they're so willing to switch days — selling them two at a time to keep the numbers whole, price falls $1 for every extra pair sold. By 20 seats, price has fallen to $20, revenue is $400, and the 19th and 20th seats together still gained $22 — more than the $20 (2 x $10) it costs to carry them. The next pair, taking it to 22, would gain only $18 combined — less than $20, so stop at 20. Leisure, profit-maximising: 20 seats at $20 = $400. Split by group, the company sells 30 seats for $300 + $400 = $700 total. Now check charging ONE price to everyone instead. At $20 a seat, 15 commuters and 20 leisure travellers buy — 35 seats — but at $10 profit each that's only $350 total, because so many commuters who'd have paid up to $48 are getting a seat for $20. At $24, only 13 commuters and 12 leisure travellers buy — 25 seats, still only $350, because now too many leisure travellers have been priced out. $22 lands in between and beats both: 14 commuters and 16 leisure travellers, 30 seats, for $22 x 30 = $660 revenue and $360 profit — the best any single price can do here. Splitting the price by group still beats even that best single price: $700 revenue and $400 profit, $40 more of each, purely from charging commuters and leisure travellers what each group was actually willing to pay instead of forcing them both to the same number.
Name the three conditions that had to hold for this to work, and why each is load-bearing, not decorative. First, monopoly power — real price-setting power over this specific journey, not necessarily zero competition (a coach exists, it's just a weaker substitute for someone who has to be at their desk by 9): without it, any price above the $10 marginal cost in EITHER group would just get undercut by a rival train operator, and the whole pricing gap would vanish through ordinary competition before resale ever became the issue. Second, a genuine difference in price elasticity of demand between the two groups — verified above, not assumed: commuters' elasticity at their $30 price and 10 seats works out to −1.5, leisure's at their $20 price and 20 seats to −2.0, so leisure really is the more price-responsive group, not just labelled that way. If both groups had the same elasticity, solving MR=MC separately in each would land on exactly the same price in both — there'd be nothing to gain from splitting them at all. Third, a way to stop leisure tickets being resold to commuters. Without it, a leisure traveller who paid $20 could sell their seat on to a commuter for, say, $25 — a bargain against the $30 commuter price, and still a profit for the seller — and every commuter would simply buy a resold leisure ticket instead of paying full price, dragging the whole market back toward something close to the $20 leisure price for everyone: roughly 30 seats at $20 is just $600, well below even the best single uniform price above. Real train operators solve this not by checking names at the door but by making the ticket types themselves incompatible: an off-peak leisure fare is simply not valid for travel before, say, 9:30am, so a resold leisure ticket physically cannot be used to board the 8am train, no ID check required.
Formally
A monopolist with power over two separable submarkets sets MRc = MC in the commuter submarket and MRl = MC in the leisure submarket independently, rather than solving for one combined MR — that independence is exactly what letting quantity and price differ by group buys the firm, and exactly what a single uniform price forces it to give up. The less elastic group always lands on the higher price: commuters, at elasticity −1.5, pay $30; leisure, at elasticity −2.0, pay $20 — because a less price-sensitive group loses relatively little demand to a price rise, so its MR stays above MC for longer as output rises, letting the firm push further up that group's own AR curve before stopping. The paragraph below states this same trio of conditions — monopoly power, differing price elasticity of demand between sub-markets, preventable resale — in the course's own formal language, and the worked chain further into this lesson runs the identical MRc = MC / MRl = MC method on a genuinely different, real-style case, in pounds, echoing the real, verified Zambia Sugar context — this time also quantifying what the split does to consumer surplus in each submarket, not just to the firm's own revenue.
(spec 3.3.3.6f) turns monopoly power into a pricing strategy rather than a single price: charging different prices to different, separately-identifiable groups of customers for what is functionally the same product. Three conditions have to hold simultaneously, not just one — genuine monopoly (or at least significant) power to set price above MC in the first place; a measurably different price elasticity of demand between the groups (if every group's elasticity were the same, marginal revenue would already be equal across groups at a single uniform price, and there'd be nothing to gain from charging different ones); and a way to stop customers in the cheaper group reselling to the more expensive one — without that, arbitrage erases the price gap the whole strategy depends on. Pearson's own real-world examples of firms actually separating customers by elasticity, rather than just asserting they can, are hotels, train companies and restaurants pricing by time of booking or day of the week — off-peak, price-sensitive customers pay less; peak, less price-sensitive customers pay more, for capacity that would otherwise sit unused. The worked example below derives exactly why, and quantifies who gains and who loses when a firm actually does this.
Natural monopoly has thin support in the real exam record: the facts bank finds exactly two brief evaluative-aside mentions of it across all 15 reviewed WEC13 series (the MTN Ghana quote above, and one further passing line in a Jun 2023 nationalisation essay), and no standalone Section B or C question built around it. That doesn't mean it's untestable — spec 3.3.3.6e is explicit — but this lesson teaches it as clean spec-definition content on purpose, and does not claim any past-paper worked-example precedent for it beyond the single verified quote used above. Do not cite this lesson as evidence that natural monopoly is a heavily-examined topic; it isn't, in the archive reviewed.
Mechanism
Why the deadweight-loss argument needs a stated competitive benchmark, not just a monopoly diagram
What an examiner is actually checking for on a monopoly-inefficiency answer isn't whether P>MC gets asserted — every candidate writes that sentence. It's whether the answer shows what P>MC is being compared AGAINST: a stated competitive benchmark output and price (where AR would meet MC directly), so the gap between the monopoly outcome and that benchmark can be named as an actual quantity of lost value, not just described as "higher prices, lower output." A response that says "the monopolist charges more and produces less than competitive firms would" is describing the shape of the problem; a response that marks Qc/Pc explicitly on the diagram and shades the triangle between Qm and Qc as value neither the firm nor consumers ever get — because those units are never produced at all — is quantifying it, which is what separates a Level 2 assertion from a Level 3+ analysis. The same move works in reverse for the benefit case: "a monopoly can achieve economies of scale" is an assertion; naming what specifically falls (LRAC, via which of the six spec-named internal sources) and what that does to the position of the AC curve relative to a smaller competing firm's is the analysis a mark scheme actually rewards.
x-axis: Output, Q · y-axis: Price and cost, £
- AR = D
- Downward-sloping — the monopolist faces the entire market demand curve directly, since it IS the market, not a stylised individual-firm slice.
- MR
- Below AR at every output, same intercept, twice the gradient — the standard AR/MR relationship derived in Business Objectives.
- AC
- U-shaped average cost, same derivation as the Costs lesson.
- MC
- U-shaped marginal cost, crossing AC at AC's minimum.
- Qm, Pm
- Monopoly profit-maximising output and price, where MR=MC; Pm read directly off AR at Qm.
- Qc, Pc (competitive benchmark)
- The hypothetical output/price if this market were instead perfectly competitive — where AR meets MC directly (P=MC). Not drawn from a second firm; it's what AR=MC would give this exact demand and cost structure.
- AC-minimum output (productive-efficiency benchmark)
- The output where AC bottoms out — here, where MC crosses AC. Qm sits well to its left, so the monopolist is producing at a higher unit cost than its own technology allows at full efficiency: a real, mark-scheme-credited productive inefficiency, distinct from the allocative P>MC result, not the same claim restated.
- Deadweight welfare loss
- The triangle bounded by AR above and MC below, between Qm and Qc — value lost because those units, worth more to consumers than they'd cost to produce, are simply never made.
- Supernormal profit rectangle
- (Pm − AC) × Qm at Qm — sustained into the long run specifically because barriers prevent the entry that would compete it away in any other structure this course has covered.
Common error: Drawing a standard AR/MR/AC/MC monopoly diagram with Qm and Pm marked, but no competitive benchmark Qc/Pc anywhere on it — leaving the deadweight-loss triangle with nothing to be measured against.
Correct: Qc/Pc marked explicitly at the AR–MC intersection alongside Qm/Pm, with the deadweight-loss triangle shaded between the two outputs, AND the AC-minimum output marked separately as the productive-efficiency benchmark — Qm sitting to its left is what makes the monopolist productively, not just allocatively, inefficient, a distinct mark-scheme point the diagram alone can carry. The diagram is the evidence for both inefficiency claims, not a label stuck onto a generic downward-sloping-demand picture.
Worked, in full
Third-degree price discrimination — deriving the conditions, then quantifying who actually gains and loses
- 01
Start from why price elasticity of demand has to differ between the two submarkets, not just exist as a label. A profit-maximising discriminating monopolist sets MR=MC separately in each submarket. If both submarkets had identical price elasticity of demand at every price, their MR curves would be identical functions of price too — meaning the single price that solves MR=MC in one submarket already solves it in the other. There would be no profit-increasing reason to charge two different prices at all. The condition isn't a rule to memorise; it's the only case where discrimination has anything to gain.
Earns: K — the PED-difference condition derived from the profit-maximising logic itself, not asserted as a spec fact to recall.
- 02
Set up a genuine numeric case, echoing the real, verified Zambia Sugar context (Oct 2020) without reproducing its figures: a firm sells to a domestic submarket with demand Pd = 80 − 2Qd (steeper — less elastic, since domestic buyers have fewer substitutes) and an export submarket with demand Pe = 50 − 0.5Qe (flatter — more elastic, since export buyers can switch supplier more easily). Constant marginal cost MC = £20 in both.
Earns: K — the numeric setup stated explicitly, with the economic reason for each slope given, not just asserted.
- 03
Solve MR=MC separately in each submarket. Domestic: TRd = 80Qd − 2Qd², so MRd = 80 − 4Qd; setting MRd = 20 gives Qd = 15, Pd = £50. Export: TRe = 50Qe − 0.5Qe², so MRe = 50 − Qe; setting MRe = 20 gives Qe = 30, Pe = £35. The firm charges the domestic (less elastic) submarket the higher price, exactly as the theory predicts — verified: domestic price elasticity of demand at this point is −1.67, export's is −2.33, so domestic genuinely is the less elastic of the two.
Earns: An1 — both submarket equilibria solved independently, with the resulting price ordering checked against the underlying elasticities rather than just assumed.
- 04
Now quantify the transfer, not just describe it. Computed directly: if this monopolist had instead been forced to charge one uniform price to both submarkets, profit-maximising behaviour on the combined (kinked) demand curve gives a single price of £38, at which domestic consumer surplus is £441 and export consumer surplus is £144 (total £585). Under discrimination, domestic consumer surplus falls to £225 (a loss of £216) while export consumer surplus rises to £225 (a gain of £81) — total consumer surplus falls to £450, a net loss of £135, even though total output is identical in both cases (45 units either way) and firm profit rises from £810 to £900. Discrimination here doesn't change how much is produced at all — it purely redistributes who buys it and at what price, and that redistribution itself destroys some surplus even without any change in output.
Earns: Eval — the actual transfer computed in figures (who loses £216, who gains £81, what happens to the total), not left as "some consumers are worse off, others better off."
In your own words
In one sentence: why does a profit-maximising discriminating monopolist need price elasticity of demand to genuinely differ between two submarkets, rather than merely needing two separate submarkets to exist?
Contestability — the spec's own answer to what disciplines a monopoly without breaking it up
(spec 3.3.3.8a) asks a different question from every other market structure this course has covered: not "how many firms are there?" but "how easily could another firm start trading here?" A perfectly contestable market has three characteristics: potential entrants face the same costs and technology as the existing firm (no structural advantage to being first), have access to the same information, and — the condition that actually does the work — can enter and exit freely, with lost if they try and fail. A market can therefore have exactly one firm trading in it right now and still behave close to competitively, if that third condition holds; a market can have several firms trading and still behave close to a protected monopoly, if it doesn't. Firm count and market behaviour are genuinely separate questions, which is precisely the fallacy the first prequestion above was built to catch.
The implication for firm behaviour (spec 3.3.3.8b) is : an incumbent in a contestable market has to set price with an eye on what price would make entry profitable for someone else, not just on what maximises its own current profit. Set price at the unconstrained monopoly level Pm, and — if sunk costs are genuinely low — a rival can enter, undercut, take sales, and exit again with little lost even if the incumbent immediately retaliates on price: "hit-and-run entry." The rational response is to price defensively, closer to average cost, sacrificing some of the profit the standard MR=MC diagram would otherwise predict — not because a rival has actually shown up, but because one credibly could. This is the mechanism the diagram below makes precise.
Costs and benefits of contestability (spec 3.3.3.8c) mirror, and partly offset, monopoly's own costs and benefits from earlier in this lesson. For consumers: prices closer to AC, output closer to the competitive level, without needing government intervention to force it — the market disciplines itself. For firms: lower sustained profit than an equivalent, genuinely protected monopoly would earn, and less funding available for the dynamic-efficiency investment the benefit case for monopoly leans on — a real cost, not just a consumer-side story. The evaluative sting: contestability's discipline depends entirely on the THREAT remaining credible. If an incumbent can find a way to raise sunk costs against potential entrants specifically (a long-term exclusive supplier contract, a costly proprietary standard, aggressive predatory pricing that punishes any entry attempt hard enough to deter the next one) the market can drift from genuinely contestable back toward a protected monopoly without its firm count ever changing.
The significance of sunk costs (spec 3.3.3.8d) is therefore not a footnote to contestability — it's the entire mechanism, and it's the direct mirror of the barriers-to-entry content from Oligopoly and the start of this lesson. A barrier that raises SUNK costs specifically (rather than just total entry costs) is the one that damages contestability most, because sunk cost is precisely the part a potential entrant can't get back if the venture fails — buying specialised, non-resellable machinery is a sunk cost; leasing the same machinery, returnable at the end of the lease, mostly isn't. The same underlying six barrier types from Oligopoly's spec point (economies of scale, limit pricing, patents, branding, sunk costs, legal restriction) can therefore be re-read through a single lens: which of them specifically raise sunk cost, and which just raise total cost without making it unrecoverable? Only the former genuinely closes off contestability; the latter can still coexist with a market that stays disciplined by threat alone.
| Stakeholder | Costs | Benefits |
|---|---|---|
| Consumers |
| |
| Firms |
|
Common error: Treating contestability's consumer benefit as automatic and permanent, or only addressing one of the two spec-named groups (firms and consumers).
Correct: Both groups addressed, plus the evaluative sting this lesson's own teach block names directly: contestability's discipline lasts only as long as the entry threat stays credible — an incumbent that raises SUNK costs specifically against potential entrants (a long-term exclusive supplier contract, a costly proprietary standard, predatory pricing severe enough to deter the next attempt) can drift the market back toward a protected monopoly without its firm count ever changing.
Mechanism
Why a credible threat disciplines price with no actual entry — and what would change that
The examiner's three-stage read on a contestability answer: what they see first is whether the answer treats the ONE firm's price as fixed by the standard monopoly diagram (weak — the firm-count fallacy) or as a response to an anticipated future, not a realised present. What they're actually looking for is the specific causal chain: low sunk costs mean a potential entrant risks little by trying, which means the incumbent has to forecast that any price high enough to yield supernormal profit is also high enough to invite that entry, which means the rational move is to price near AC continuously, before any rival ever appears — not react to one after the fact. What would change the decision, and is worth stating explicitly in an evaluation: if sunk costs were high instead — specialised, non-transferable machinery a rival would have to buy outright and couldn't resell if the attempt failed — the same incumbent could safely set the full unconstrained monopoly price, because the threat that disciplined it in the low-sunk-cost case is no longer credible. The whole model turns on one number (how much is genuinely lost on exit), not on how many firms happen to be trading today.
x-axis: Output, Q · y-axis: Price and cost, £
- AR = D
- Same market demand curve as the monopoly diagram above — the firm's underlying market position hasn't changed.
- MR
- Below AR at every output, as before.
- AC
- U-shaped average cost, same curve as above.
- MC
- U-shaped marginal cost, crossing AC at AC's minimum, same curve as above.
- Qm, Pm (unconstrained monopoly point)
- Carried over from the diagram above, shown for direct comparison — this is what the firm would charge if entry were not a credible threat at all.
- QL, PL (limit price and output)
- Set where AR meets AC — the highest price at which a potential entrant, facing the same AC curve, could expect at best only normal profit from entering. Below Pm, above the unconstrained firm's own AC minimum.
- The sacrificed rectangle
- The supernormal profit given up by pricing at PL instead of Pm — the explicit, costed trade-off the incumbent accepts in exchange for a lower probability (or speed) of entry. This is what makes limit pricing a genuine strategic choice, not just 'a lower price'.
Common error: Drawing only the limit-price point, with no unconstrained Pm/Qm shown for comparison — the deliberate sacrifice the incumbent is making becomes invisible, and the diagram reads as 'a firm that happens to charge a low price' rather than a strategic response to a threat.
Correct: Both the unconstrained monopoly point and the limit price/output shown on the same diagram, with the limit price tied to a specific stated benchmark (AC, or a named potential entrant's own expected cost) — the whole point of the diagram is to make the trade-off visible, not just the outcome.
Complete it yourself
Complete the chain — from low sunk costs to limit pricing, with no actual entry
- 01
A market has only one firm operating, but potential entrants could lease rather than buy all the capital equipment needed to enter, and could resell any unused stock or transfer any licence on exit — sunk costs of entry are close to zero.
- 02
Because almost nothing is lost by trying and failing, a potential entrant can attempt hit-and-run entry: enter while the incumbent's price is high enough to make entry profitable, take some sales and profit, then exit again with little cost if the incumbent responds by cutting price.
Named traps
- increase-vs-decrease-in-contestability
- Confirmed directly in an Oct 2023 examiner report on a contestability MCQ: "This is a topic that candidates find difficult to understand, and they should ensure they know the difference between an increase and decrease in contestability." The concrete version of this error: treating any policy change as automatically raising contestability. Deregulation and lower sunk-cost requirements raise it; a merger between two of the few credible potential entrants, or a new licensing requirement, lowers it. Read the specific mechanism described, don't default to a direction.
- naming-is-not-applying
- A document from this course's own prior build attributed to WEC13 examiner reports, presented as an exact quotation repeated across multiple series: "Just writing a company name in the answer does not merit application." That precise sentence was independently re-checked this session against all 13 published examiner reports for this paper and appears in none of them — a fabricated quote with a false citation, corrected here rather than carried forward. The real idea it was dressed up to support does hold, though: examiner reports consistently reward data actually USED to justify a claim, not merely named. Compare "MTN Ghana is a monopoly, so it's inefficient" (naming) against the real mark scheme's own move, quoted in full above: "Monopolies will not be allocatively efficient as the lack of competition, such as MTN Ghana controlling 70% of the market, allows them to charge higher prices (P>MC)" — the 70% figure is doing real work in that sentence, not sitting next to the argument unused.
- conditions-vs-benefits-of-price-discrimination
- The spec splits third-degree price discrimination into two separate sub-points — the CONDITIONS necessary for it (3.3.3.6f: monopoly power, differing PED, preventable resale) and its COSTS AND BENEFITS (3.3.3.6g: firm revenue, consumer surplus effects, off-peak capacity use). A response that only explains why a firm CAN price-discriminate, without reaching what it actually does to firms and consumers once it does, has answered half the spec point — the same structural pattern Oligopoly's own lesson flags for limit pricing appearing in two separate sub-points of that spec item. Check which half, or both, the question is actually asking for.
- no-competitive-benchmark-caps-the-level
- Every WEC13 essay mark scheme checked this session caps a response below the top level without the diagram a question specifically calls for — and on monopoly specifically, 'a diagram' means one with the competitive benchmark (Qc, Pc) marked alongside the monopoly outcome (Qm, Pm), not just a standard AR/MR/AC/MC picture with nothing to compare it against. Without the benchmark, the deadweight-loss argument has nothing to point at. On a price-discrimination question, it means both submarkets' MR=MC diagrams shown, not one drawn and the other only described in prose.
- no-named-industry-caps-level-4-kaa
- A second, separate gate from the diagram requirement above, confirmed in the real Oct 2021 examiner report on this exact MTN Ghana monopoly-inefficiency essay, verbatim: "Answers to this question could only secure a Level 4 KAA mark if they referred to an industry in their answers." A diagram alone is necessary but not sufficient for the top KAA band — the analysis has to be tied to a specific, named real (or clearly stated hypothetical) industry throughout, matching the "For an industry of your choice" instruction every real WEC13 monopoly/contestability essay of this type carries in its own command line. The level-exemplar below names one from Level 3 onward for exactly this reason.
- unconditional-conclusion
- "Monopoly is always harmful to consumers" and "a contestable market never needs regulation" are both unconditional claims, and — consistent with every other WEC13 essay type checked this session — an unconditional conclusion caps evaluation below the top band regardless of how strong the knowledge underneath it is. State the condition in the same sentence as the conclusion: see the conditional-judgement drill below for exactly what that move looks like on both halves of this lesson.
The conditional move
Complete: "Third-degree price discrimination raises total welfare, not just firm profit, only if ___."
Complete: "A monopoly is unlikely to need direct government intervention to protect consumers only if ___."
Beyond the spec
The spec asks you to describe what makes a market contestable and to name the conditions for third-degree price discrimination, without naming either the theory that first formalised 'discipline without actual competition' or the economist who first split price discrimination into named degrees at all. Both close a real gap: without them, 'contestability' and 'third-degree' read as vocabulary to memorise rather than the output of a specific, checkable argument someone had to build first.
William Baumol, John Panzar and Robert Willig's Contestable Markets and the Theory of Industry Structure (1982) is the paper this lesson's whole second half is built on: their central result is that a market can be disciplined toward competitive, or near-competitive, pricing purely by the THREAT of entry, with no rival ever actually operating in it, provided entry and exit are free — specifically, provided sunk costs are low enough that a potential entrant risks little by trying. Their most striking conclusion is that a genuinely 'perfectly contestable' monopoly — zero sunk costs, instant entry and exit — is forced to price at exactly the competitive level even with only one firm actually trading, which is the theoretical extreme the limit-pricing diagram above is a real-world approximation of. Separately, the reason this spec point is called specifically THIRD-degree price discrimination, not just 'price discrimination,' traces to Arthur Pigou's The Economics of Welfare (1920), which first classified discrimination by how finely a firm can separate its customers: first-degree (a different price for every individual unit or customer — perfect discrimination, mostly a theoretical benchmark), second-degree (different prices for different QUANTITY blocks bought by the same customer, e.g. bulk discounts), and third-degree — the only one WEC13 actually examines — different prices for different, separately-identifiable GROUPS of customers, exactly the domestic/export split worked through above. Knowing there are two other degrees the exam doesn't test is itself useful: it's what stops a student from reaching for the third-degree conditions on a scenario that's actually describing bulk discounts or fully individualised pricing instead.
Retrieval — with feedback on every choice
A monopolist faces market demand P = 150 − Q and has constant marginal cost of £30. What price does it charge at its profit-maximising output, and how does this compare with marginal cost?
Which of the following best describes a natural monopoly?
A regulator changes the rules for a market so potential entrants can now lease, rather than being required to buy, all the specialised equipment needed to enter. What is the most likely effect on the market's contestability, and why?
A domestic airline has been the only carrier on a regional route for a decade, earning supernormal profit every year. Regulations require any new entrant to lease, not buy, its aircraft — leases are returnable with no penalty at the end of the term — and airport landing slots on this route are available to any airline that applies. A rival airline is known to have both the capital and the aircraft leases needed to enter within weeks, if the incumbent's price ever rose enough to make entry worthwhile.
Using the concept of contestability, explain why the incumbent airline is likely to price below its unconstrained profit-maximising monopoly price on this route, despite facing no actual current competitor.
Same question, every level
For an industry of your choice, evaluate the view that a monopoly is always harmful to consumers. Illustrate your answer with an appropriate diagram(s). (VERIDIAN-original question, written in the style of real WEC13 monopoly essays confirmed across the archive reviewed for this course — including the "for an industry of your choice" command phrasing and the diagram instruction, both verified verbatim on the real Oct 2021 MTN Ghana monopoly-inefficiency essay — not a reproduction of any single past paper question.)
20 marks available
A monopoly is when there's only one firm in a market. Monopolies are bad for consumers because they can charge high prices since there's no competition.
Descriptive, no formula, no diagram, no named industry despite the question requiring one, no named mechanism — 'no competition' asserts the conclusion without showing why that specifically produces a higher price than the alternative.
- Monopoly: MR=MC on AR=D (the whole market). P > MC. Barriers block entry, so profit persists into the long run.
- Monopoly harm isn't only P>MC: productive inefficiency (Qm below AC-min), X-inefficiency (cost drift passed to price), and product-quality decline are three separate, separately-creditable channels. Benefit case includes EoS, dynamic efficiency, AND cross-subsidising loss-making lines.
- Third-degree PD needs: monopoly power + different PED per group + no resale between groups. Higher price to the LESS elastic group.
- Natural monopoly: LRAC still falling across all realistic demand — thin exam record, teach as definition, not past-paper precedent.
- Contestability: low/no sunk costs + credible entry threat → limit pricing near AC. Firm count ≠ behaviour.
- No competitive benchmark on the diagram, no named industry, or an unconditional conclusion — each caps a monopoly essay below top level (verified: Level 4 KAA needs a named industry, not just a diagram).
Not affiliated with or endorsed by Pearson Edexcel. Every quotation and figure attributed to a mark scheme or examiner report in this lesson was independently verified against the primary Pearson document, not carried over from prior course material. The numeric price-discrimination example is VERIDIAN-original, computed directly rather than asserted; no real past-paper question is reproduced anywhere in this lesson.
A monopolist faces market demand P = 150 − Q and has constant marginal cost of £30. What price does it charge at its profit-maximising output, and how does this compare with marginal cost?
- Q = 60, P = £90 — above marginal cost
Correct. TR = 150Q − Q², so MR = 150 − 2Q. Setting MR = MC: 150 − 2Q = 30 → Q = 60, P = 150 − 60 = £90. £90 is well above the £30 marginal cost — the P>MC result guaranteed by AR=D sloping downward for a monopolist.
- BQ = 60, P = £90 — equal to marginal cost
The output Q=60 is right, but the price is £90, not £30 — asserting P=MC here ignores that this is a monopolist facing a downward-sloping demand curve, not a price-taking competitive firm.
- CQ = 120, P = £30
This solves P=MC directly (150−Q=30), which is the competitive price-taking condition, not the monopolist's actual profit-maximising rule MR=MC. A monopolist doesn't set P=MC voluntarily — check which condition the question is actually asking about.
- DQ = 40, P = £110
Check MR at Q=40: MR = 150 − 2(40) = £70, not £30 — this doesn't satisfy MR=MC at all. Recompute 150−2Q=30 directly rather than estimating.
Traps tested: Asserts p equals mc anyway · Treats monopolist as price taker · Arithmetic slip
Which of the following best describes a natural monopoly?
- Long-run average cost keeps falling across the entire range of output the market could realistically demand, so one firm can supply the whole market more cheaply than two or more competing firms could
Correct. This is the specific cost-structure claim spec 3.3.3.6e names — not just 'a monopoly that occurs naturally,' but a market where splitting demand between rival firms is genuinely more expensive than one firm supplying it all.
- BA market protected by a government-granted legal monopoly, such as a patent or an exclusive licence
This describes a legal barrier to entry — a real, spec-named barrier type, but a different mechanism entirely from a natural monopoly's cost-structure origin.
- CA single firm that has grown large enough to buy out or force out every rival in its market
This describes how a firm might BECOME a monopoly through its own conduct — mergers, aggressive competition. A natural monopoly's defining feature is its underlying cost structure, not the history of how it got there.
- DA firm that allows its average costs to drift above the minimum achievable because it faces no competitive pressure
This is the definition of X-inefficiency, a genuinely different concept — a natural monopoly can be fully productively efficient at its own falling-LRAC scale; X-inefficiency is about slack, not cost structure.
Traps tested: Confuses natural and legal monopoly · Confuses natural monopoly with conduct · Confuses with x inefficiency
A regulator changes the rules for a market so potential entrants can now lease, rather than being required to buy, all the specialised equipment needed to enter. What is the most likely effect on the market's contestability, and why?
- Contestability rises, because leased equipment can be returned rather than lost on exit — sunk costs fall, making hit-and-run entry a more credible threat
Correct. This is close to the textbook definition of what raises contestability: lowering the amount a potential entrant genuinely loses if the attempt fails, which is exactly what sunk cost measures.
- BContestability falls, because a firm that only leases equipment has weaker long-term commitment to the market, which discourages entry
'Commitment' isn't the mechanism contestability theory turns on — what matters is how much is unrecoverably lost if the firm exits, and leasing directly lowers exactly that.
- CContestability is unchanged, because the market still has only one firm actually trading in it
The number of firms currently trading doesn't determine contestability on its own — what changed here is the cost of trying and failing, which is the actual mechanism.
- DContestability falls, because the incumbent no longer has unique assets to defend, which entrenches its position further
This doesn't follow from what actually changed — the rule change affects POTENTIAL ENTRANTS' costs, not the incumbent's asset ownership, and lower entrant costs raise, not lower, the credibility of entry.
Traps tested: Confuses commitment with sunk cost · Firm count fallacy · Garbled causal reasoning
A domestic airline has been the only carrier on a regional route for a decade, earning supernormal profit every year. Regulations require any new entrant to lease, not buy, its aircraft — leases are returnable with no penalty at the end of the term — and airport landing slots on this route are available to any airline that applies. A rival airline is known to have both the capital and the aircraft leases needed to enter within weeks, if the incumbent's price ever rose enough to make entry worthwhile.
Using the concept of contestability, explain why the incumbent airline is likely to price below its unconstrained profit-maximising monopoly price on this route, despite facing no actual current competitor.
- Because sunk costs of entry are low (leased, not purchased, aircraft; open landing slots) and a credible rival can enter quickly, the market is contestable — the incumbent sets a limit price closer to average cost to deter hit-and-run entry, sacrificing some current profit rather than risking the whole route to a fast entrant, even though it remains the only firm actually operating
Correct, and this is the fully-integrated version: it names the specific mechanism lowering sunk costs (leased aircraft, open slots), states the incumbent's rational response (limit pricing near AC), and explains why this happens without any actual rival ever entering.
- BBecause government price regulation directly caps the fare on this specific route, forcing marginal-cost pricing
Nothing in the stimulus describes price regulation on this route — this invents a mechanism the scenario doesn't support, rather than using the sunk-cost and entry-threat detail it actually gives.
- CBecause it is the only airline on the route, it is a natural monopoly, and natural monopolies always price at average cost
The stimulus describes low sunk costs and a credible entry threat — the contestability mechanism — not a falling-LRAC cost-structure claim, which is what natural monopoly actually is. It also overclaims: natural monopolies don't automatically price at AC without regulation forcing it.
- DBecause only one airline actually operates the route, this is by definition an uncontested monopoly, and its price will remain at the standard monopoly profit-maximising level regardless of any potential rival
This is exactly the firm-count fallacy the stimulus is built to test: it ignores the leased aircraft, open landing slots, and credible rival the scenario explicitly gives, all of which are what actually determine pricing behaviour here.
Traps tested: Invents unstated regulation · Conflates natural monopoly with contestability · Firm count fallacy
Practice this for real
This site teaches the mechanism; the exam is sat on Pearson's own real questions. Go find and attempt these yourself — nothing here substitutes for actually sitting a timed paper.
Pearson's official past-papers portalSelect International Advanced Level → Economics → any series, then look for WEC13.
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