In which of the following market structures would X-inefficiency be most likely to exist? Perfect competition. Monopoly. Oligopoly. Monopolistic competition.

Monopoly

Explanation:

Monopoly is a market structure where only one firm controls the market share and earn abnormal profits. In a monopoly market, a producer or a supplier earn abnormal profits, which is why they don't try to control the cost of production because they can sell the good at any price. This situation where the cost of production increases, it creates X-inefficiency.