In this talk, we will model sequential听auctions听in financial markets and study the efficiency of this kind of market mechanisms听compared with limit order books. In this type of market orders of market participants are received during a period of time. At the end of this duration, a clearing price of the听auction听is determined as the price maximizing the exchanged volume at the clearing time according to the supply and demand of each market participant. We will first focus on the optimal duration of an听auction听to reduce the error between the clearing price and the efficient price of the stock considered and compute the optimal duration of the听auctions听for some stocks traded on Euronext.听We then extend the study to a new market mechanism 鈥渁d hoc electronic听auction听design鈥 (AHEAD) in which market participants have the opportunity to trigger the听auction听instead of waiting for the opening of the听auction. We will finally study some possible flaws of听auction听markets and the remedies in terms of regulation policy we can adopt.听