We analyze the role of liquidity and collection of information in order to measure the speed of revelation of information during the preopening of order-driven markets. We extend Vives (1995) model to the case where risk averse traders receive a new private signal before each round of quotation of the preopening. We show that price discovery takes place at high speed which is consistent with the empirical studies of Biais, Hillion and Spatt (1999)