Although the aggregate capital share of U.S. firms has increased, the firm-level capital share of a typical U.S. firm has decreased. This divergence is due to mega-firms that now produce a larger output share without a proportionate increase in labor compensation. We develop a model in which firms insure workers against firm-specific shocks, where more productive firms allocate more rents to shareholders, while less productive firms endogenously exit. Increasing firm-level risk delays exit and increases the measure of mega-firms, which raises the aggregate capital share while lowering the average firm's capital share. An increase in the level of rents quantitatively magnifies this effect. We present evidence supporting this mechanism.
