This paper studies the design of ex ante efficient mechanisms in situations where a single item is for sale, and agents have positively interdependent values and can covertly acquire information at a cost before participating in a mechanism. I find that when interdependency is low and/or the number of agents is large, the ex post efficient mechanism is also ex ante efficient. In cases of high interdependency and/or a small number of agents, ex ante efficient mechanisms discourage agents from acquiring excessive information by introducing randomization to the ex post efficient allocation rule in areas where the information’s precision increases most rapidly.