Final answer:
Collusion by oligopolists can involve cartels, informal understandings, and price leadership, all aimed at reducing output and raising prices to increase profits.
Step-by-step explanation:
Three major means of collusion by oligopolists are cartels, informal understandings, and price leadership. This question pertains to the strategic behaviors that firms in an oligopoly might engage in to control market conditions and maximize their profits. A cartel is a group of firms that formally agree to collude in order to produce and sell products as if they were a monopoly. Informal understandings refer to agreements that are not written or explicitly stated but are understood among firms in the industry. Price leadership is a strategy used by one dominant firm in the market that sets the price level that other firms follow, thus indirectly coordinating prices without formal agreement. These practices aim to reduce output and keep prices high, which can be more profitable for the firms involved but can also lead to legal issues and market inefficiencies.