Long-Run Equilibrium for Monopolists: Sustaining Market Power

In most markets, high profits are a signal – they invite competition, draw in new firms, and eventually bring prices back down. But what happens when that mechanism simply doesn’t work? In a monopoly, barriers to entry mean that no new competitor can step in, no matter how attractive the profits look. This changes everything about how a firm behaves in the long run. A monopolist doesn’t just survive over time – it can actively design its output level, plant size, and pricing strategy to protect and grow its advantage. Understanding this long-run equilibrium is key to understanding how monopolistic market power is built and sustained.

How the long run differs for a monopolist 🔗

In competitive markets, the long run acts as an equalizer. New firms enter when profits are high, supply increases, prices fall, and eventually everyone earns only normal profit. The monopolist, however, operates in a fundamentally different environment. In the long run, a monopolist has the time to expand its plant or to use its existing plant at any level that maximizes profit. With entry blocked, there is no pressure to reach an optimal scale or to drive costs down to their minimum.

This is the core distinction: in markets with significant barriers to entry, it is not necessarily true that high profits will attract new firms, or that their entry will eventually cause prices to fall to a normal profit level in the long run. The monopolist is, in a real sense, insulated from the competitive forces that discipline other firms.

What keeps competitors out? 🔗

Monopoly power in the long run depends on the durability of its barriers to entry. These barriers include economies of scale that lead to natural monopoly, control of a physical resource, legal restrictions on competition, patent and trademark protection, and practices like predatory pricing that intimidate potential competitors. In agriculture and agribusiness, a firm that controls a critical input – say, a patented seed variety or proprietary fertilizer formula – can maintain this kind of protection for years. Similarly, control of natural resources that are critical to the production of a final good is a prime source of monopoly power.

Once these protections are in place, the monopolist can operate across the long run with a degree of freedom that no competitive firm enjoys – choosing plant size, output level, and price in ways that maximize profit rather than minimize cost.

The equilibrium condition: LMC = MR 🔗

The foundation of long-run equilibrium for a monopolist is the same profit-maximizing rule used in the short run, but now applied across the full flexibility of the long run. A monopoly firm maximizes profit at the output level where long-run marginal cost (LMC) equals marginal revenue (MR), and the LMC curve intersects the MR curve from below. This condition ensures that the firm is neither producing too little (where MR exceeds LMC and more output would add to profit) nor too much (where LMC exceeds MR and additional output destroys profit).

It’s worth noting why marginal revenue is always less than price for a monopolist. Because the firm faces a downward-sloping demand curve, it must lower its price on all units sold – not just the additional one – to sell more. This creates a permanent gap between price and marginal revenue, which is precisely where monopoly profit lives.

In the long run, the firm will operate at a point on the long-run average cost curve where the short-run average cost curve is tangent to it – because it is only at such a tangency point that short-run marginal cost equals long-run marginal cost. This makes the selected plant size genuinely optimal for the given level of demand, even if it doesn’t correspond to the minimum of the long-run average cost curve.

Two conditions for valid long-run equilibrium 🔗

For a monopolist to be in a true long-run equilibrium, two conditions must be satisfied simultaneously. First, LMC must equal MR (the profit-maximizing output condition). Second, the long-run average revenue (AR) must be greater than or equal to long-run average cost (LAC) – meaning the firm must at least be covering all its costs. A monopolist earning losses in the long run will eventually exit the market, so sustained participation requires at least normal profit.

Plant size and the three possible outcomes 🔗

One of the most important insights about monopoly in the long run is that there is no single, predetermined plant size a monopolist must adopt. A monopolist may reach the optimal scale at the minimum point of the long-run average cost (LAC) curve, remain at a suboptimal scale on the falling part of the LAC, or surpass the optimal scale and expand beyond the minimum LAC – depending entirely on market demand conditions.

These three scenarios can be summarized as follows:

Suboptimal plant with excess capacity: When market demand is limited, the monopolist may operate with a plant that is smaller than the cost-minimizing size, and even that smaller plant may be underutilized. This is a common scenario in niche agricultural input markets where demand simply doesn’t justify full-scale production.

Optimal plant at minimum LAC: In rare cases, market demand is just large enough to allow the monopolist to build the ideal plant and run it at full capacity. This results in the most cost-efficient outcome, though it doesn’t mean the monopolist charges a competitive price.

Oversized plant with overutilization: When market size is very large, the monopolist may build a plant larger than the optimal size and overutilize it – this is often the case with public utility companies operating at a national level. Such a plant leads to higher costs both because it exceeds optimal scale and because it is run beyond efficient capacity.

In each case, the output decision is still governed by the LMC = MR condition. Plant size is simply the instrument the monopolist uses to best position itself for that output level.

Supernormal profits in the long run 🔗

The most striking outcome of monopoly in the long run is the persistence of supernormal profits – returns above and beyond what is needed to keep the firm in the industry. In competitive markets, such profits disappear as rivals enter. In a monopoly, with entry blocked, they do not. A monopolist will most probably continue to earn supernormal profits in the long run, given that entry is barred.

Graphically, this is shown when the equilibrium price (set on the demand/AR curve above the LMC = MR point) exceeds the long-run average cost at that output level. The gap between price and average cost, multiplied by the quantity produced, is the supernormal profit. This holds because at equilibrium, LMC = MR, but LAC is less than AR – meaning average revenue exceeds average cost.

However, there is one scenario where even a monopolist earns only normal profit in the long run: when cost and demand conditions are such that AR exactly equals LAC at the equilibrium output. In this case, total revenue just covers total cost. The monopolist stays in business, but earns no economic surplus beyond the normal return.

Excess capacity: a deliberate feature, not a flaw 🔗

A competitive firm, in the long run, is forced to produce at the minimum point of its average cost curve – full efficiency is the price of survival. A monopolist faces no such constraint. Instead, monopolists routinely operate with excess capacity, meaning they produce less than the output level that would minimize average costs.

Under monopoly, because restrictions on entry and exit exist, firms can earn abnormal profits, and the long-run average cost is not necessarily minimized at the equilibrium output level. The profit-maximizing output, set where LMC = MR, typically falls short of the cost-minimizing output. This means the firm’s average cost at equilibrium is higher than it theoretically needs to be – a direct consequence of market power rather than productive inefficiency.

From a social welfare perspective, this excess capacity represents a real cost. Resources – labor, capital, land – are tied up in production facilities that are not being used to their fullest potential. Under imperfect competition, installed capacity is often not fully used, meaning total output is less than what is socially desirable and resources lie idle. The monopolist, however, has no incentive to correct this, since operating below minimum efficient scale is entirely consistent with maximizing long-run profit.

Excess capacity as a competitive deterrent 🔗

Beyond cost structure, excess capacity also serves a strategic function. A monopolist that visibly maintains production capacity beyond current output signals to any would-be entrant that it could rapidly increase supply and drive down prices. This threat alone can be enough to discourage new firms from attempting entry – making excess capacity a market control tool as much as a cost outcome.

Price, efficiency, and the broader impact 🔗

Long-run monopoly equilibrium has significant implications for market efficiency. The condition that marginal revenue equals marginal cost is used to determine the profit-maximizing level of output for every firm – but for a monopolist, this results in a price that exceeds marginal cost, unlike in perfect competition where price equals marginal cost at equilibrium.

This price mark-up over marginal cost is the source of what economists call deadweight loss – potential transactions that would have benefited both buyer and seller but never occur because the monopolist’s price is too high for some consumers. The monopolist captures profit; society loses efficiency. In agribusiness contexts – where monopolistic control over seeds, chemicals, or distribution networks can affect food access and farm income – this trade-off carries real-world significance well beyond the textbook.

Additionally, unlike a competitive firm that achieves productive efficiency by operating at minimum average cost, a monopolist in long-run equilibrium is productively inefficient, since it does not produce at the minimum point of its average cost curve. The combination of allocative and productive inefficiency makes monopoly equilibrium a persistent concern for policymakers and regulators.

The threat of entry and limit pricing 🔗

Even when formal barriers protect a monopolist, the threat of potential competition is never entirely absent. When that threat becomes credible – when a well-resourced firm starts eyeing the market – the monopolist may respond by lowering its price toward the level of long-run average cost. If a threat of entry arises, the monopolist may adopt a price reduction strategy, lowering price to the level where it earns only normal profit, specifically to deter new entrants. This behavior, known as limit pricing, sacrifices some short-run profit in exchange for preserving the monopoly position in the long run.

This strategic flexibility – the ability to adjust price, output, and plant size in response to market signals – is what makes the monopolist’s long-run position so durable. It is not passive; it is actively managed.

What do you think? Given that monopolists can sustain supernormal profits indefinitely by controlling plant size and output, should regulators focus more on breaking up monopolies or on controlling the prices they charge? And in agribusiness specifically – where a handful of firms control key inputs like seeds and agrochemicals – does the concept of “excess capacity as strategy” concern you from a food security standpoint?

References

1. https://www.economicsdiscussion.net/monopoly/equilibrium-of-the-monopolist-short-run-and-long-run-equilibrium/5310
2. https://psu.pb.unizin.org/agbm101/chapter/9-1-how-monopolies-form-barriers-to-entry/
3. https://courses.lumenlearning.com/suny-fmcc-microeconomics/chapter/how-monopolies-form-barriers-to-entry/
4. https://en.wikipedia.org/wiki/Monopoly
5. https://www.scribd.com/document/55931156/Long-Run-Equilibrium-Under-Monopoly
6. https://www.yourarticlelibrary.com/economics/monopoly/the-long-run-equilibrium-under-monopoly/37220
7. https://economicshelpdesk.com/micro/long-period-equilibrium.php
8. https://www.geeksforgeeks.org/microeconomics/long-run-equilibrium-under-perfect-monopolistic-and-monopoly-market/
9. https://en.wikipedia.org/wiki/Monopolistic_competition
10. https://analystprep.com/cfa-level-1-exam/economics/long-run-equilibrium-under-each-market-structure/
11. https://www.vaia.com/en-us/explanations/microeconomics/imperfect-competition/perfect-competition-vs-monopolistic-competition/