We compare two mechanisms for selling IPOs, the fixed price method and American book-building, when investors have correlated information and can observe each other's subscription decisions. In this environment, the fixed price method is a strategy that can create cascading demand. Alternatively, and underwriter building a book aggregates investor information into the offer price. We find that bookbuilding generates higher expected proceeds but exposes the issuer to greater uncertainty, and that it provides the option to sell additional shares that are not underpriced on the margin.