Let’s consider a bit more formally how price discrimination affects economic welfare.
We begin by assuming that the monopolist can price discriminate perfectly.
Perfect price discrimination describes a situation in which the monopolist knows exactly
the willingness to pay of each customer and can charge each customer a different
price. In this case, the monopolist charges each customer exactly his
willingness to pay, and the monopolist gets the entire surplus in every transaction.
Figure 15-10 shows producer and consumer surplus with and without price
discrimination. Without price discrimination, the firm charges a single price above
marginal cost, as shown in panel (a). Because some potential customers who value
the good at more than marginal cost do not buy it at this high price, the monopoly
causes a deadweight loss. Yet when a firm can perfectly price discriminate, as
shown in panel (b), each customer who values the good at more than marginal cost
buys the good and is charged his willingness to pay. All mutually beneficial trades
take place, there is no deadweight loss, and the entire surplus derived from the
market goes to the monopoly producer in the form of profit.