In this paper, we study the optimal provision of a costly public good using an average efficiency crite-
rion. For every fixed cost, we identify a quota mechanism as the optimal mechanism among those that are
dominant-incentive-compatible, deficit-free and kind. Moreover, we also consider the asymmetric case and
demonstrate that a committee mechanism is optimal for a large class of mechanisms. In particular, this
mechanism dominates all VCG (pivotal) mechanisms.