  I characterize the consumer-optimal market segmentation in competitive
markets where multiple firms selling differentiated products to consumers with
unit demand. This segmentation is public---in that each firm observes the same
market segments---and takes a simple form: in each market segment, there is a
dominant firm favored by all consumers in that segment. By segmenting the
market, all but the dominant firm maximally compete to poach the consumer's
business, setting price to equal marginal cost. Information, thus, is being
used to amplify competition. This segmentation simultaneously generates an
efficient allocation and delivers to each firm its minimax profit.
