Markets With Only a Few Sellers Because of the few sellers, the key feature of oligopoly is the tension between cooperation and self-interest Harcourt, Inc. items and derived items copyright o 2001 by Harcourt, IncHarcourt, Inc. items and derived items copyright © 2001 by Harcourt, Inc. Markets With Only a Few Sellers Because of the few sellers, the key feature of oligopoly is the tension between cooperation and self-interest