📚 Behaviour of Oligopolistic Firms | 寡头垄断企业的行为
Oligopoly is one of the most realistic and complex market structures featured in Cambridge A-Level Economics. It describes a market dominated by a small number of large firms, where each firm's decisions are strategically linked to the expected reactions of its rivals. This article explores the behaviour of oligopolistic firms, covering interdependence, collusive and non-collusive models, game theory, pricing strategies, non-price competition, and efficiency evaluation.
寡头垄断是剑桥 A-Level 经济学中最贴近现实也最复杂的市场结构之一。它描述的是由少数大型企业主导的市场，每家企业的决策都与其对竞争对手反应的预期紧密相连。本文探讨寡头垄断企业的行为，涵盖相互依赖、合谋与非合谋模型、博弈论、定价策略、非价格竞争以及效率评价。
1. What is Oligopoly? | 什么是寡头垄断？
Oligopoly is a market structure characterised by a few dominant firms that hold a significant share of market supply. The exact number of firms is not fixed, but the key feature is that each firm's actions directly affect rivals, creating strategic interdependence. Industries like petrol retailing, mobile networks, commercial banking, and supermarket chains are typical examples in many economies.
寡头垄断是一种市场结构，由少数占据较大市场份额的主导企业构成。企业数量没有固定标准，但关键特征是每家企业的行为都会直接影响竞争对手，从而形成策略上的相互依赖。汽油零售、移动通信网络、商业银行和连锁超市等行业是许多经济体中典型的寡头例子。
2. Key Characteristics of Oligopoly | 寡头的关键特征
Oligopolistic markets share several defining features. First, high concentration ratios (often a five-firm concentration ratio above 60%) indicate that a small number of firms control most output. Second, significant barriers to entry – such as economies of scale, brand loyalty, and legal restrictions – protect the position of existing firms. Third, products may be homogeneous (e.g., steel, cement) or differentiated (e.g., cars, smartphones). Most importantly, firms are interdependent, meaning their pricing and output decisions cannot be made in isolation.
寡头市场具有若干共同特征。第一，高集中度比率（通常五企业集中度高于 60%）表明少数企业控制了大部分产出。第二，显著的进入壁垒——如规模经济、品牌忠诚度和法律限制——保护了现有企业的地位。第三，产品可以是同质的（如钢铁、水泥）或差异化的（如汽车、智能手机）。最关键的是，企业之间相互依赖，意味着定价和产量决策无法独立做出。
3. Interdependence and Strategic Behaviour | 相互依赖与策略行为
Because there are only a few major players, each oligopolist must continuously anticipate how rivals will respond to any change in price, output, or marketing. This interdependence leads to strategic behaviour, where firms try to maximise their own profits while taking into account the likely moves of competitors. A price cut might trigger a price war, undermining profits for all; a price rise might only be followed if rivals are confident it will stick. This creates a strong incentive for non-price competition and can explain why prices in oligopolies are often stable.
由于只有少数主要参与者，每个寡头企业都必须不断预测竞争对手会如何应对价格、产量或营销上的任何变化。这种相互依赖导致了策略行为，企业试图最大化自身利润，同时考虑竞争对手的可能行动。降价可能引发价格战，损害所有企业的利润；涨价则可能只有在竞争对手确信涨幅能够维持时才会跟进。这为非价格竞争提供了强烈动机，也可以解释寡头市场中的价格为何常常保持稳定。
4. Game Theory and the Prisoner's Dilemma | 博弈论与囚徒困境
Game theory provides a useful framework for analysing interdependent decision-making in oligopoly. The prisoner's dilemma is a classic example. Consider two firms, A and B, each deciding whether to charge a high price or a low price. The payoff matrix (in terms of profit) might look like this:
博弈论为分析寡头中的相互依赖决策提供了有用的框架。囚徒困境便是一个经典例子。假设有 A 和 B 两家企业，各自决定是定高价还是定低价。其收益矩阵（以利润表示）可能如下：
| Firm B: High Price | Firm B: Low Price | |
| Firm A: High Price | A: £10m, B: £10m | A: £2m, B: £15m |
| Firm A: Low Price | A: £15m, B: £2m | A: £6m, B: £6m |
If both firms set a high price, they each earn £10 million. If one undercuts while the other keeps prices high, the undercutter captures more market share and earns £15 million, while the high-price firm earns only £2 million. If both set low prices, they end up with £6 million each. The dominant strategy for each firm is to choose a low price, leading to a Nash equilibrium that is worse for both than mutual cooperation. This illustrates the tension between individual rationality and collective interest in oligopoly.
如果两家企业都定高价，各自获利 1000 万英镑。如果一方降价而另一方维持高价，降价者抢走市场份额，获利 1500 万英镑，而高价企业仅获利 200 万。如果双方都定低价，则各自只得 600 万。每家企业的占优策略都是选择低价，最终形成一个对双方都不如合作理想的纳什均衡。这揭示了寡头中个体理性与集体利益之间的紧张关系。
5. Collusive Oligopoly: Cartels | 合谋寡头：卡特尔
To avoid the destructive effects of price competition, firms may engage in collusion – an explicit or tacit agreement to coordinate prices, output, or market sharing. A formal collusive agreement is known as a cartel. The most famous example is the Organization of the Petroleum Exporting Countries (OPEC), which attempts to set production quotas to influence global oil prices. Collusion allows oligopolists to act like a joint monopolist, restrict total output, raise prices, and maximise combined profits. However, cartels are inherently unstable because each member has an incentive to cheat by secretly lowering price or exceeding quotas. In many countries, cartels are illegal under competition law.
为了避免价格竞争的破坏性影响，企业可能进行合谋——通过明示或默示协议协调价格、产量或市场分配。正式的合谋协议称为卡特尔。最著名的例子是石油输出国组织 (OPEC)，它试图设定生产配额以影响全球油价。合谋使寡头企业能够像一个联合垄断者那样行动，限制总产量，抬高价格，并最大化联合利润。然而，卡特尔天生不稳定，因为每个成员都有动机通过秘密降价或超配额生产来作弊。在许多国家，卡特尔根据竞争法属于非法。
6. Non-Collusive Oligopoly: The Kinked Demand Curve | 非合谋寡头：弯折的需求曲线
When firms do not collude, their behaviour can be modelled by the kinked demand curve theory. This model assumes that if a firm raises its price, rivals will not follow, causing the firm to lose a large share of sales – making demand relatively elastic above the current price. Conversely, if a firm lowers its price, rivals will match the cut to protect their market share, so the firm gains little extra sales – making demand relatively inelastic below the current price. This creates a kink in the demand curve at the prevailing market price.
当企业不合谋时，其行为可以用弯折的需求曲线理论来建模。该模型假设：如果一家企业提高价格，竞争对手不会跟进，导致该企业丧失大量销售——使得需求在当前价格以上相对富有弹性。相反，如果一家企业降价，竞争对手会同步降价以保护市场份额，因此该企业新增的销量很少——使得需求在当前价格以下相对缺乏弹性。这在现行市场价格处造成了需求曲线的弯折。
Demand curve: P₁ → elastic above, inelastic below
需求曲线：P₁ 以上富有弹性，以下缺乏弹性
The discontinuity in the marginal revenue curve that results from the kink means that significant shifts in marginal cost may not lead to a change in profit-maximising price and output. This helps explain observed price rigidity in oligopolistic markets.
弯折导致边际收益曲线出现间断，意味着边际成本的大幅变动可能不会引起利润最大化价格和产量的变化。这有助于解释寡头市场中观察到的价格刚性现象。
7. Price Rigidity in Oligopoly | 寡头中的价格刚性
Empirical evidence often shows that prices in oligopolistic industries change less frequently than in more competitive markets. The kinked demand curve provides one explanation: firms fear that raising prices will lose customers, while cutting prices will just spark retaliation without much gain. Additionally, administrative costs of changing prices (menu costs), customer dissatisfaction from frequent changes, and the desire to avoid price wars contribute to price stability. Instead, firms focus on non-price competition to increase market share.
经验证据通常表明，寡头行业的价格变动频率低于更具竞争性的市场。弯折的需求曲线提供了一种解释：企业担心提价会失去顾客，而降价只会引发报复却收益甚微。此外，变更价格的管理成本（菜单成本）、频繁变动导致的顾客不满，以及避免价格战的愿望，都促成了价格稳定。因此，企业转而依靠非价格竞争来扩大市场份额。
8. Non-Price Competition | 非价格竞争
Because price competition can be mutually destructive, oligopolists commonly compete through product differentiation, advertising, branding, loyalty schemes, after-sales service, and innovation. Heavy spending on marketing and R&D is a hallmark of many oligopolistic industries, from smartphones to soft drinks. Non-price competition can increase consumer choice and drive product improvements, but it can also create wasteful duplication and act as a barrier to entry by raising the sunk costs needed to compete effectively.
由于价格竞争可能两败俱伤，寡头企业通常通过产品差异化、广告、品牌建设、忠诚度计划、售后服务和创新来竞争。从智能手机到软饮料，大量的营销与研发支出是许多寡头行业的标志。非价格竞争可以增加消费者选择并推动产品改进，但也可能造成浪费性重复，同时通过提高有效竞争所需的沉没成本而构成进入壁垒。
9. Barriers to Entry and Limit Pricing | 进入壁垒与限制性定价
High barriers to entry help sustain long-run supernormal profits in oligopoly. Natural barriers include economies of scale that make it costly for new entrants to achieve low unit costs. Artificial barriers include aggressive strategies such as limit pricing, where incumbent firms set prices low enough to discourage entry but still above average cost. Predatory pricing – temporarily pricing below cost to force rivals out – is another possible strategy, although it is illegal in many jurisdictions. Heavy advertising and control over supply chains also raise entry barriers.
高进入壁垒有助于维持寡头企业在长期中的超额利润。自然壁垒包括规模经济，这使得新进入者难以实现低单位成本。人为壁垒包括诸如限制性定价等激进策略，即现有企业将价格定得足够低以阻止新企业进入，但仍高于平均成本。掠夺性定价——暂时将价格定在成本以下以排挤对手——是另一种可能的策略，尽管在许多司法管辖区属于非法。大量的广告投入以及对供应链的控制也会抬高进入壁垒。
10. Oligopoly and Efficiency | 寡头与效率
Oligopoly outcomes are mixed from an efficiency standpoint. Allocative efficiency is likely to be violated because price tends to remain above marginal cost (P > MC). Productive efficiency may not be achieved if firms enjoy monopoly power that protects them from cost-minimising pressures. However, oligopolists often benefit from significant economies of scale that can reduce unit costs below what a more fragmented industry could achieve. Dynamic efficiency – investment in innovation and new technology – can be high in oligopolies if firms use supernormal profits to fund R&D. Thus, while oligopoly often leads to welfare losses compared with perfect competition, it can also deliver gains in terms of innovation and product variety.
从效率角度看，寡头的结果是复杂的。配置效率很可能无法实现，因为价格往往高于边际成本 (P > MC)。如果企业凭借垄断势力免受成本最小化的压力，生产效率也可能无法达到。但寡头企业通常受益于显著的规模经济，这可能将单位成本降至更分散的行业无法实现的水平。如果企业将超额利润用于研发，寡头市场中的动态效率——即对创新和新技术的投资——可能很高。因此，虽然与完全竞争相比寡头常常导致福利损失，但在创新和产品多样性方面也能带来收益。
11. Evaluation of Oligopoly | 对寡头垄断的评价
Oligopoly is often considered the most prevalent market structure in modern economies. Whether it serves consumer welfare depends on the degree of competition. Where collusion is effective, prices can be high and output restricted, harming consumers. In non-collusive oligopolies, the outcome is closer to that of monopolistic competition, with moderate mark-ups but high non-price competition. Governments often intervene through competition policy to prevent cartels, monitor mergers, and investigate abuse of dominance. The overall assessment must weigh the costs of possible consumer exploitation against the benefits of scale, innovation, and stability that large oligopolistic firms can provide.
寡头垄断通常被认为是现代经济中最常见的市场结构。它是否有利于消费者福利取决于竞争程度。在有效的合谋下，价格可能高企、产量受限，损害消费者。在非合谋寡头中，结果更接近垄断竞争，价差适中但非价格竞争激烈。政府常常通过竞争政策进行干预，以防止卡特尔、审查并购并调查滥用支配地位的行为。全面评价必须在可能损害消费者的代价与大型寡头企业所能提供的规模经济、创新和稳定性等好处之间进行权衡。
Published by TutorHao | Economics Revision Series | aleveler.com
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