As auction based mechanisms for electricity dispatch are emerging in previously regulated electricity supply industries, it is imperative to understand the effect of auction rules and structure on efficiency. In this paper, I analyze the ability of different auction structures to induce the efficient dispatch in a framework where generators know their own and opponents' costs with certainty. In particular, I am interested in identifying which, if any, rules in an auction structure are necessary and sufficient to guarantee the efficient dispatch in equilibrium. I find that the auction mechanism chosen for California cannot guarantee productive efficiency in equilibrium. The main failing of the California action design is the way in which demand is bundled and hence the way bids are defined. I show that, while an auction mechanism which allows for more than one winner in an auction cannot guarantee efficiency, an auction where there is exactly one winner can guarantee that all pure-strategy equilibria are efficient.