The paper characterizes the mixed-strategy equilibria in all-pay auctions with endogenous prizes that depend positively on own e?ort and negatively on the e?ort of competitors. Such auctions arise naturally in the context of investment games, lobbying games, and promotion tournaments. We also provide an experimental analysis of a special case which captures the strategic situation of a two-stage game with investment preceding homogenous Bertrand competition. We obtain overinvestment both relative to the mixed-strategy equilibrium and the social optimum.