This article quantifies the impact of Wal-Mart Supercenters on supermarkets’ profitability via a two-stage dynamic entry game, using method of simulated moments and milk scanner data from Dallas/Fort Worth supermarkets. The empirical findings show that the entry of Wal-Mart Supercenters accounts for about an average 50% decrease in milk profit margins for incumbent supermarkets. Effects of scale are found to be more significant for Wal-Mart Supercenters than for incumbent supermarkets, granting Wal-Mart a competitive edge.