We compare the incentive of an incumbent monopolist to deter the entry
between Cournot and Bertrand competition in differentiated product
markets. It is first shown that unless the products are perfect substitutes, the
incumbent can block the entry more easily under Cournot competition than
under Bertrand competition. For the entry deterrence, as long as the
products are differentiated to some degree, like the blockaded entry, the
incumbent would like to deter the entry more under Cournot competition
than under Bertrand competition. However, if the product differentiation is
quite small, the incumbent can deter the entry more easily under Bertrand
competition than in the Cournot competition.