It often happens that a monopolist finds it possible and profitable to sell a single commodity at different prices to different buyers. This can occur when he is selling in several markets which are divided from one another in such a way that goods which are sold in the cheaper market cannot be bought from the monopolist and resold in the dearer market; and when customers in the dearer market cannot transfer themselves into the cheaper market to get the benefit of the lower price. The act of selling the same article, produced under a single control, at different prices to different buyers is known as price discrimination.