A monopsonist faces an upward-sloping supply curve L^S, implying that its marginal expenditure curve, ME, is above the supply curve. It hires labor quantity l_m at point a, where its marginal expenditure (its marginal cost of labor) equals its MRP_L (its marginal benefit of labor). It pays a wage W_m at point b, the height of the supply curve at that quantity of labor l_m. A set of perfectly competitive firms facing the same supply curve would hire the labor quantity l_c and pay a wage W_c. The deadweight loss of monopsony, area DWL, arises because there will be some workers who would work for wages that are lower than the marginal revenue product they create for the firm, but are not hired because doing so would raise overall wages too much. The deadweight loss represents the labor that is not sold in the monopsonist market, which would be sold in the competitive market. This lost social surplus equals DWL, the area between the MRP_L and labor supply curves for labor units between l_m and l_c.