Oligopoly | 寡头垄断

📚 Oligopoly | 寡头垄断

Oligopoly is a market structure dominated by a small number of large firms, each holding a significant share of the market. These firms are interdependent, meaning the actions of one firm directly affect the others. In IGCSE AQA Economics, you need to understand the key features, behaviour and evaluation of oligopolies, as well as how they compete and sometimes collude. This article covers the essential points in a clear, structured way.

寡头垄断是一种由少数几家大企业主导的市场结构，每家企业都占据显著的市场份额。这些企业相互依赖，一家企业的行为会直接影响其他企业。在IGCSE AQA经济中，你需要理解寡头的关键特征、行为及评价，以及它们如何竞争、有时又如何勾结。本文将以清晰的结构梳理所有核心考点。

1. Definition and Key Characteristics | 定义与关键特征

An oligopoly exists when a few large firms dominate the market, each with enough market power to influence price but not enough to ignore rivals’ reactions. The key characteristics include: a high concentration ratio, product differentiation or homogeneity, significant barriers to entry, and strong interdependence among firms.

当少数几家大企业主导市场，且每家企业都拥有足以影响价格但无法忽视对手反应的市场势力时，就形成了寡头。关键特征包括：高集中度比率、产品差异化或同质化、显著的进入壁垒，以及企业间强烈的相互依赖。

Oligopolies can sell differentiated or homogeneous products. For example, the car industry has differentiated products (brands and models), while the steel or cement industry sells nearly identical goods. Barriers to entry – such as economies of scale, high capital costs, brand loyalty and control of technology – protect the incumbent firms from new competitors.

寡头可以销售差异化或同质化的产品。例如，汽车行业提供差异化产品（品牌和型号），而钢铁或水泥行业销售几乎相同的商品。进入壁垒——如规模经济、高资本成本、品牌忠诚度和技术控制——保护在位企业免受新进入者的威胁。

Interdependence is the defining behavioural feature. Because there are only a few sellers, each firm must consider how its rivals will respond to any change in price, output or marketing. This often leads to strategic behaviour and can result in price rigidity or collusion.

相互依赖是寡头行为的决定性特征。由于卖家数量很少，每家企业都必须考虑竞争对手对其价格、产量或营销变化的反应。这常常导致策略性行为，并可能引起价格刚性或勾结。

2. Concentration Ratios | 集中度比率

A concentration ratio measures the combined market share of the largest firms in the industry. The most common is the five-firm concentration ratio (CR5) – the percentage of total market sales accounted for by the top five firms. A high concentration ratio indicates an oligopolistic or even monopolistic market.

集中度比率衡量行业内最大企业的市场份额总和。最常用的是五企业集中度比率（CR5）——即前五大企业占总市场销售额的百分比。高集中度比率表明寡头甚至垄断市场。

For instance, if the total market sales are £100 million and the top five firms sell £78 million, the CR5 = 78%. In the UK, definitions vary, but a CR5 above 60% often signals an oligopoly. The higher the ratio, the more market power the leading firms possess and the less competitive the industry tends to be.

例如，若市场总销售额为1亿英镑，前五家企业销售额为7800万英镑，则CR5 = 78%。在英国，定义可能不同，但CR5超过60%通常意味着寡头结构。比率越高，主导企业的市场势力越大，行业竞争性越弱。

You can also use a three-firm ratio (CR3) or even an eight-firm ratio depending on the analysis. These ratios help competition authorities assess the potential for collusion and anti-competitive behaviour. When evaluating oligopolies, distinguish between a high concentration ratio alone and actual abuse of market power.

你也可以使用三企业比率（CR3）甚至八企业比率，视分析需求而定。这些比率帮助竞争监管机构评估勾结和反竞争行为的可能性。评价寡头时，要区分单纯的高集中度比率与实际滥用市场支配力之间的差别。

3. Interdependence and Game Theory | 相互依赖与博弈论

Interdependence means a firm’s decisions depend heavily on the expected reactions of rivals. This can be analysed using simple game theory, particularly the prisoner’s dilemma. In a duopoly (two-firm oligopoly), each firm can choose a high-price or low-price strategy. The best collective outcome is often to keep prices high, but the fear of being undercut by the rival can drive both to adopt low prices, leading to a worse outcome for all.

相互依赖意味着企业的决定在很大程度上依赖于对竞争对手反应的预期。这可以通过简单的博弈论来分析，尤其是囚徒困境。在双头垄断（双企业寡头）中，每家企业可以选择高价或低价策略。对集体最有利的结果通常是维持高价，但担心被对手削价抢走市场，可能促使双方都采取低价，导致对所有人都不利的结局。

The payoff matrix below illustrates this dilemma. Assume two firms, A and B. If both charge high prices, they each earn £10m. If both charge low, each earns £4m. If one charges high while the other charges low, the high-price firm earns £2m while the low-price firm captures the market and earns £12m. The dominant strategy for each firm is to lower the price, leading to a Nash equilibrium where both end up with £4m instead of the collusive £10m.

下面的收益矩阵说明了这一困境。假设企业A和B。如果都定高价，各赚1000万英镑；如果都定低价，各赚400万。如果一方高价而另一方低价，高价企业只赚200万，而低价企业占领市场赚1200万。每家企业的主导策略是降价，从而形成纳什均衡——双方最终只得到400万而非合谋下的1000万。

Firm B
High Price | Low Price
Firm A High Price: (10, 10) | (2, 12)
Firm A Low Price: (12, 2) | (4, 4)

This model explains why cartels are unstable even without legal enforcement, and why oligopolists often avoid price wars through non-price competition or tacit collusion.

这个模型解释了为何即使没有法律强制，卡特尔依然不稳定，也解释了为什么寡头常常通过非价格竞争或默契合谋来避免价格战。

4. Price Rigidity and the Kinked Demand Curve | 价格刚性与折弯需求曲线

One famous model that predicts price stability in oligopoly is the kinked demand curve. The assumption is that if a firm raises its price, rivals will not follow, so the firm will lose many customers – demand is elastic above the prevailing price. If a firm lowers its price, rivals will match the cut to protect their market share, so the firm gains few new customers – demand is inelastic below the current price. This creates a ‘kink’ at the existing price.

预测寡头价格稳定性的一个著名模型是折弯需求曲线。假设是：如果一家企业提价，竞争对手不会跟进，因此该企业会失去大量顾客——在当前价格之上需求富有弹性。如果一家企业降价，竞争对手会跟着降价以保护市场份额，因此该企业只会获得极少的新顾客——在当前价格之下需求缺乏弹性。这就在现有价格处形成了一个“折弯”。

The kinked demand curve helps explain why oligopolists often keep prices constant even when costs change. The marginal revenue curve has a discontinuous vertical gap at the kink, meaning marginal cost can shift within this gap without causing a price change. Hence, firms compete using advertising, brand loyalty and product design instead of price.

折弯需求曲线有助于解释为什么寡头即使成本变化也常常维持价格不变。边际收益曲线在折弯处有一个不连续的垂直缺口，意味着边际成本可以在该缺口内移动而不会引起价格变化。因此，企业转而通过广告、品牌忠诚度和产品设计等非价格手段竞争。

However, the kinked demand curve has been criticised for not explaining how the initial price is set, only why it might stay fixed. Despite this, it remains a useful tool for understanding price rigidity and the role of non-price competition.

然而，折弯需求曲线被批评为没有解释初始价格是如何设定的，只解释了为何可能保持稳定。尽管如此，它仍是理解价格刚性和非价格竞争作用的有用工具。

5. Non-price Competition | 非价格竞争

Because price wars can be mutually destructive, oligopolistic firms often engage in non-price competition. This involves advertising, branding, loyalty schemes, product innovation, packaging, after-sales service, and sponsorship. The aim is to increase market share without triggering a direct price response from rivals.

由于价格战可能两败俱伤，寡头企业经常采取非价格竞争。这包括广告、品牌建设、忠诚度计划、产品创新、包装、售后服务和赞助等。其目的是在增加市场份额的同时避免引发竞争对手的直接价格回应。

Advertising can create strong brand loyalty, making demand less price-elastic. Product differentiation through R&D allows a firm to charge a premium. For example, smartphone manufacturers constantly add new features (cameras, battery life, AI tools) to distinguish their models. Even in more homogeneous markets, firms compete on delivery times, quality consistency, and technical support.

广告能营造强烈的品牌忠诚度，使需求对价格的敏感度降低。通过研发实现的产品差异化使企业能够收取溢价。例如，智能手机制造商不断添加新功能（摄像头、电池寿命、AI工具）来区分产品。即使在较为同质化的市场，企业也会在交货时间、质量一致性和技术支持上竞争。

Non-price competition can benefit consumers through better quality and more choice, but it can also waste resources if advertising merely cancels out rivals’ efforts. Exams often ask you to evaluate whether non-price competition increases allocative and dynamic efficiency.

非价格竞争可通过更高的质量和更多选择惠及消费者，但如果广告仅仅是抵消对手的努力，也可能浪费资源。考试中常会要求评价非价格竞争是否提高了配置效率和动态效率。

6. Collusion: Overt and Tacit | 勾结：公开与默契

Collusion occurs when firms cooperate rather than compete. Overt collusion happens when firms make a formal agreement to fix prices, limit output, share markets, or restrict entry. This is typically illegal in most countries. Tacit collusion is more subtle – firms implicitly coordinate behaviour without explicit communication, often by following price leadership.

当企业合作而非竞争时，就发生了勾结。公开勾结是指企业达成正式协议，固定价格、限制产量、瓜分市场或限制进入。这在大多数国家通常是违法的。默契合谋则更加隐蔽——企业无需明确沟通，常常通过追随价格领导者的方式暗中协调行为。

An example of overt collusion is a cartel. Price leadership – where the dominant firm sets a price and others follow – is a form of tacit collusion that can be hard to prove. Parallel pricing, where all firms charge very similar prices without coordination evidence, also raises suspicion but may simply reflect competitive benchmarking.

公开勾结的一个例子是卡特尔。价格领导制——主导企业制定价格，其他企业跟随——是一种难以证明的默契合谋形式。平行定价，即所有企业在没有协调证据的情况下收取非常相似的价格，也会引起怀疑，但也可能仅仅反映了竞争性对标。

When evaluating collusion, consider both the incentives to collude (higher joint profits) and the incentives to cheat (individual gain from undercutting). This tension is a central insight from game theory and helps explain why many cartels collapse.

评价勾结时，既要考虑合谋的激励（更高的联合利润），也要考虑作弊的激励（削价带来的个体收益）。这种张力是博弈论的核心洞见，有助于解释为什么许多卡特尔会瓦解。

7. Cartels | 卡特尔

A cartel is a group of firms that explicitly agree to control output and fix prices, effectively acting as a monopoly. The most famous international cartel is OPEC, which coordinates oil production among member countries to influence global prices. Cartels aim to maximise joint profits by reducing output and raising price above the competitive level.

卡特尔是一组明确同意控制产量和固定价格的企业集团，实际上像一个垄断者那样行动。最著名的国际卡特尔是OPEC（石油输出国组织），它协调成员国石油产量以影响全球价格。卡特尔旨在通过减少产量将价格提高到竞争水平之上，从而实现联合利润最大化。

For a cartel to succeed, several conditions must hold: high barriers to entry prevent outsiders from increasing supply, demand for the product must be inelastic, the agreement must be enforceable, and members must not cheat. Even within OPEC, members often exceed their quotas, undermining the cartel’s effectiveness.

卡特尔要成功，必须满足几个条件：高进入壁垒阻止外部企业增加供应，产品需求必须缺乏弹性，协议必须可执行，且成员不能作弊。即使在OPEC内部，成员也常常超出配额，削弱了卡特尔的效力。

Competition authorities actively investigate and penalise cartels. In the UK, the Competition and Markets Authority (CMA) can impose fines of up to 10% of global turnover. You should be able to discuss the effects of cartels on consumers (higher prices, less choice) and on overall welfare (deadweight loss).

竞争监管机构积极调查并处罚卡特尔。在英国，竞争与市场管理局（CMA）可处以最高全球营业额10%的罚款。你应该能够讨论卡特尔对消费者（更高价格、更少选择）和整体福利（无谓损失）的影响。

8. Advantages of Oligopoly | 寡头的优点

Oligopolies can bring significant benefits to the economy. Large firms benefit from economies of scale, lowering average costs and potentially leading to lower prices for consumers if competition is strong. They often engage in dynamic efficiency by investing heavily in research and development (R&D) to create innovative products and processes. Supernormal profits provide the funds for such investment.

寡头能为经济带来显著好处。大企业受益于规模经济，降低平均成本，如果竞争激烈，有可能导致消费者价格降低。它们通常追求动态效率，大量投资研发以创造创新产品和工艺。超额利润为此类投资提供了资金。

Product differentiation gives consumers a wide variety of choice, from smartphones to cars to financial services. Non-price competition can improve quality, safety and environmental performance. Moreover, large oligopolistic firms often provide stable employment and contribute significantly to exports and tax revenues.

产品差异化让消费者拥有广泛的选择，从智能手机到汽车再到金融服务。非价格竞争可以提升质量、安全性和环境表现。此外，大型寡头企业往往提供稳定的就业，并对出口和税收做出重大贡献。

However, these benefits depend on the intensity of rivalry. When oligopolists collude rather than compete, many advantages evaporate, and consumers bear the cost.

然而，这些好处取决于竞争的激烈程度。当寡头选择合谋而非竞争时，许多优点便消失殆尽，成本由消费者承担。

9. Disadvantages of Oligopoly | 寡头的缺点

The main drawback is the potential for oligopolies to act like monopolies, restricting output and charging higher prices. Collusion – whether overt or tacit – can lead to higher profits at the expense of consumer surplus. Price rigidity may mean prices do not fall when costs decline, and allocative inefficiency (P > MC) persists.

主要缺点是寡头有可能像垄断者那样行动，限制产量并收取更高的价格。勾结——无论是公开还是默契——都能以牺牲消费者剩余为代价换取更高利润。价格刚性意味着当成本下降时价格未必下降，配置效率（P > MC）持续存在。

High barriers to entry protect inefficient firms and stifle new ideas. Although oligopolies may spend on R&D, they can also become complacent and invest merely in defensive advertising or wasteful product differentiation. Furthermore, oligopolistic market power can lead to political lobbying that harms public interest.

高进入壁垒保护了低效企业，压制了新思维。尽管寡头可能在研发上投入，但也可能变得自满，只投资于防御性广告或浪费性的产品差异化。此外，寡头的市场势力可能导致有损公共利益的政治游说。

In extreme cases, oligopolistic firms may use predatory pricing – temporarily lowering prices below cost – to drive out rivals and then raise prices again. This anti-competitive strategy reinforces the importance of effective competition policy.

在极端情况下，寡头企业可能使用掠夺性定价——短暂地将价格降至成本以下——以驱逐竞争对手，然后再提高价格。这种反竞争策略凸显了有效竞争政策的重要性。

10. Evaluation and Real-World Examples | 评价与现实案例

Whether an oligopoly delivers net benefits depends on the circumstances. A concentrated market with vigorous non-price competition and high innovation (e.g. the smartphone industry) can be very beneficial. In contrast, a concentrated market with tacit collusion and high entry barriers (e.g. some energy or banking markets) may harm consumers.

寡头是否带来净收益取决于具体情况。一个集中度高但非价格竞争激烈、创新活跃的市场（如智能手机产业）可能非常有利。相反，一个集中度高且存在默契合谋、高进入壁垒的市场（如某些能源或银行业）可能损害消费者。

Real-world examples include the UK supermarket industry, dominated by Tesco, Sainsbury’s, Asda and Morrisons (CR4 historically high). Supermarkets compete on price, product range, convenience and loyalty programmes, but there have been investigations into collusion on petrol pricing. The global smartphone market (Apple, Samsung, Huawei, Xiaomi) illustrates intense non-price rivalry and rapid innovation. The airline industry on many routes shows oligopolistic features, with price wars and parallel pricing both observed.

现实案例包括由Tesco、Sainsbury’s、Asda和Morrisons主导的英国超市行业（CR4历史上很高）。超市在价格、产品种类、便利性和忠诚度计划上竞争，但也曾就汽油定价被揭露勾结。全球智能手机市场（苹果、三星、华为、小米）展示了激烈的非价格竞争和快速创新。许多航线上的航空业也表现出寡头特征，价格战和平行定价并存。

When evaluating exam questions, always use analytical chains – for example, ‘High concentration may lead to collusion, which raises prices and reduces consumer surplus, but if non-price competition is strong, consumers may still gain from better quality. The outcome depends on the contestability of the market and the effectiveness of regulation.’ This balanced approach will earn top marks.

在回答考试评价类问题时，务必使用分析链条——例如，“高集中度可能导致勾结，从而抬高价格并减少消费者剩余，但如果非价格竞争激烈，消费者仍可能从更好的质量中获益。结果取决于市场的可竞争程度和监管的有效性。”这种平衡的分析方法能为你赢得高分。

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Oligopoly | 寡头垄断