(When) are mixed markets good for consumers?

Are consumers best served in a purely private regime with efficient but profit-maximizing private firms, a purely public regime with inefficient but welfare-maximizing public firms, or a mixed regime comprising both efficient private firms and welfare-oriented public firms? In standard symmetric oligopolies (e.g., homogeneous product Cournot and differentiated Bertrand) consumer surplus (CS) is highest either when all firms are public or when all firms are private. A mixed regime never delivers the maximum CS. When firms exhibit innate cost heterogeneity unrelated to ownership, mixed markets can fare better than both public and private regimes when high-cost firms are privatized. A mixed regime where only relatively low-cost firms are private is never in the best interest of consumers and indeed can be worse than a fully public or fully private regime. As a by-product of our analysis, we uncover a possible non-monotone relationship between competition and privatization under Cournot, and a novel regime-contingent best response function under Bertrand competition.