This study analyzes a free entry oligopoly under general demand and cost functions via a differential game approach. We consider an open-loop dynamic oligopoly and a memoryless closed-loop dynamic oligopoly with sticky prices. The results show under some assumptions that the number of firms at the steady state in the open-loop dynamic oligopoly is fewer than the number of firms in the static equilibrium, and that the number of firms in the memoryless closed-loop dynamic oligopoly is fewer than the number of firms in the open-loop dynamic oligopoly.