Cooperative advertising is a key incentive offered by a manufacturer to influence retailers’ promotional decisions. We study cooperative advertising in a dynamic retail oligopoly where a manufacturer sells his product through N competing retailers. We model the problem as a Stackelberg differential game in which the manufacturer announces his shares of advertising costs of the N retailers or his subsidy rates, and the retailers in response play a Nash differential game in choosing their optimal advertising efforts over time. We obtain the feedback equilibrium solution consisting of the optimal advertising policies of the retailers and manufacturer’s subsidy rates. We identify key drivers that influence the optimal subsidy rates and, in particular, obtain the conditions under which the manufacturer will not support the retailers. For the special case of two retailers we obtain insights on some key supply chain issues. First, we analyze its impact on profits of channel members and the extent to which it can coordinate the channel. Second, we investigate the case of an anti‐discrimination act which restricts the manufacturer to offer equal subsidy rates to the two retailers.