We study an experimental market in which the structure of the information flows is endogenized. When making an offer, traders choose not only the price at which they are prepared to trade, but also the subset of traders they want to inform about the offer. This design allows for two extreme institutions as special cases. If traders always inform every other trader about each offer, the resulting institution is equivalent to a double auction. If, on the other hand, traders always inform only one other trader about each offer, the resulting institution is equivalent to a decentralized bargaining market. The institution that actually evolved in the experiments, however, was in between the two extreme cases. Subjects typically informed all trad...