We compute the “applications elasticity” as a proxy for firm-level labor supply elasticity by regressing the applications to a given job on the posted wage. The average applications elasticity in our data is 0.42. We then relate our elasticity estimates to concentration in labor markets defined by six-digit SOC occupations and commuting zone. We show a robust negative relationship between the two. Applications elasticity is near zero for all but the most densely populated labor markets, suggesting that 80 percent of the workforce works in labor markets where employers exercise significant monopsony power.