Abstract. The paper is concerned with a continuum model of the limit order book, viewed as a noncooperative game for n players. An external buyer asks for a random amount X > 0 of a given asset. This amount will be bought at the lowest available price, as long as the price does not exceed a given upper bound P . One or more sellers offer various quantities of the asset at different prices, competing to fulfill the incoming order, whose size is not known a priori.The first part of the paper deals with solutions to the measure-valued optimal pricing problem for a single player, proving an existence result and deriving necessary and sufficient conditions for optimality. The second part is devoted to Nash equilibria. For a general class of random variables X and an arbitrary number of players, the existence and uniqueness of the corresponding Nash equilibrium is proved, explicitly determining the pricing strategy of each player. For a different class of random variables, it is shown that no Nash equilibrium can exist.The paper also describes the asymptotic limit as the total number of players approaches infinity, and provides formulas for the price impact produced by an incoming order.Key words. measure-valued optimization, optimality conditions, Nash equilibrium, bidding game, optimal pricing strategy, limit order book, price impact AMS subject classifications. 49K21, 49J21, 91A06, 91A13, 91A60.1. Introduction. This paper is concerned with a continuum model of the limit order book in a stock market, viewed as a noncooperative game for n players. Our main goal is to study the existence and uniqueness of a Nash equilibrium, determining the optimal bidding strategies of the various agents who submit limit orders.We consider a one-sided limit order book. In our basic setting, we assume that an external buyer asks for a random amount of X > 0 of shares of a certain asset. This external agent will buy the amount X at the lowest available price, as long as this price does not exceed a given upper bound P . One or more sellers offer various quantities of this asset at different prices, competing to fulfill the incoming order, whose size is not known a priori.Having observed the prices asked by his competitors, each seller must determine an optimal strategy, maximizing his expected payoff. Of course, when other sellers are present, asking a higher price for a stock reduces the probability of selling it.In our model we assume that the i-th player owns an amount κ i of stock. He can put all of it on sale at a given price, or offer different portions at different prices. In general, his strategy will thus be described by a measure µ i on IR + , where µ i ([0, p]) denotes the total amount of shares put on sale by the i-th player at a price ≤ p.In practice, it is clear that prices can take only a discrete set of values. However, by studying a continuum model where strategies are described by Radon measures one obtains clear-cut results on existence or non-existence of Nash equilibria, and clean, explicit solution formulas. In ge...