  We present an analysis of advertising activities in a dynamic oligopoly with
differentiated goods by differential game approach under general demand and
cost functions. Mainly we show the following results. The comparison of the
open-loop solution and that of the closed-loop solution depends on whether the
outputs of the firms are strategic substitutes or strategic complements, and
the memoryless closed-loop solution and the feedback solution are equivalent
when there is no spillover effect of advertising activities.
