This paper provides a quantitative model consistent with the theory and evidence in which pharmacy benefit management on behalf of insurance plans serves these and other purposes in both monopoly and oligopoly provider settings. Calibrating the model to the U.S. market, Casey Mulligan conclude that pharmacy benefit management is worth at least $145 billion annually beyond its resource costs. PBM services add at least $192 billion annually in value to society compared to a manufacturer price-control regime. Requiring all PBM services to be self-provided by plan sponsors would forgo about 40 percent of the net value of PBM services largely by increasing management costs.