This paper analyzes the effects of investment in advertising in the
three-stage entry game model with one incumbent and one potential entrant
firm. It is shown that if a game theory is applied, under particular
conditions, advertising can be used as a strategic weapon in the market entry
game. Depending on the level of the advertising interaction factor,
conditions for over-investment in advertising for strategic purposes are
given. Furthermore, three specific cases are analyzed: strictly predatory
advertising, informative advertising and the case when one firm?s advertising
cannot directly influence the other firm's profit. For each of them,
depending on the costs of advertising and marginal costs, equilibrium is
determined, and conditions under which it is possible to deter the entry are
given. It is shown that if the value of the advertising interaction factor
increases, power of using advertising as a weapon to deter entry into the
market decreases. Thus, in the case of informative advertising, advertising
cannot be used as a tool for deterring entry into the market, while in the
case of predatory advertising, it can. Also, we have proved that in the case
of strictly informative advertising an over-investment never occurs, while in
the two other cases, there is always over-investment either to deter or to
accommodate the entry.