Extant studies of cooperative advertising mainly consider a single-manufacturer-single-retailer channel structure.This can provide limited insights,because a manufacturer,in real practices,usually deals with multiple retailers simultaneously.In order to examine the impact of the retailers multiplicity on channel members decisions and on total channel efficiencies,this paper develops a multiple-retailer model.In this model,the manufacturer and the retailers play a Stackelberg game to make the optimal advertising decisions.Based on the quantitative results,it is observed that:1) When there are multiple symmetric retailers,as the number of retailers scales up,th.e manufacturers national advertising investment contributes increasingly to add to channel members profits in equilibrium,but the total channel efficiency deteriorates quickly and converges down to a certain value; 2) When there are multiple asymmetric retailers,the distribution channel suffers from the manufacturers uniform participation strategy due to the retailers free-riding,and benefits with the manufacturers retailer-specific participation strategy.This study derives equilibrium solutions in closed form for all games considered and measures explicitly the gains/losses of channel efficiencies under different game settings.