寡头垄断指少数厂商占有大部分市场的情况。如果大公司所拥有的巨大的内部规模经济效应使其对于小公司拥有的成本优势,便会发生全球寡头垄断。需要由比较优势以外的理论解释的一个主要的现代贸易现象是大量发生于工业化国家之间的贸易,其中很大一部分是非常相似产品之间的交换(产业内贸易)。这一在现代贸易中向传统理论提出挑战的第二个重要现象,是对高度竞争国际市场假设的一种偏离。 Oligopoly refers to the situation in which a minority of firms occupy most of the market. A global oligopolistic monopoly can occur if the large internal economies of scale large companies have make them have a cost advantage over smaller firms. A major modern trade phenomenon that needs to be explained by theories other than comparative advantages is the large-scale trade that takes place between industrialized countries, a large part of which is the exchange of very similar products (intra-industry trade). This second important phenomenon, which challenged the traditional theory in modern trade, is a deviation from the highly competitive international market assumption.