DUOPOLY There are cases in which two sellers, instead of one, control the entire supply of a broadly defined commodity, or enough of it to enable them to augment their profits by limiting output and raising price. Here the existence of a second seller affords every buyer an alternative source of supply. But it is unlikely to afford him any real alternative in quality, service, price, or terms of sale. If the two sellers are of equal strength, each must shape his policy with an eye to the action of the other. If they are of unequal strength, the weaker will usually follow the lead of the stronger. In either case, an understanding governing production and price is readily to be attained. In their essential character and in their ultimate effects, duopoly and monopoly are the same.