This paper measures the degree of monopsony power exerted by Wal-Mart over retail workers using a dominant-firm model and data in the 48 contiguous U.S. states for counties where the company operates, presenting for the first time a measure of the company’s anticompetitive behavior. Empirical results show that Wal-Mart’s monopsony power over workers varies significantly across the country, being higher in non-metro and rural counties, particularly in the south. For instance, Wal-Mart’s buying power index in labor markets in rural southern and central states is estimated to be 5% or higher while the impact on northeastern states’ retail wages is negligible.