Comparative static analysis is presented for three Cournot models, that is, Cournot oligopoly, Cournot oligopsony and Cournot oligopoly coexistent with Cournot oligopsony. Comparative statics for the first two models are made possible by taking into account the diagrams which determine simultaneously the industry quantity and product or factor price, and that for the third model by considering simultaneous determination of the equilibrium industry output and factor demand.