Exchange-mandated discrete pricing restrictions create a wedge between the underlying equilibrium price and the observed price. This wedge permits a competitive market maker to realize economic profits that could help recoup fixed costs. The optimal tick size that maximizes the expected profits of the market maker can equal to $1/8 for reasonable parameter values. The optimal tick size is decreasing in the degree of adverse selection. Discreteness per se can cause time-varying bid-ask spreads, asymmetric commissions, and market breakdowns. Discreteness, which imposes additional transaction costs, reduces the value of private information. Liquidity traders can benefit under certain conditions.

[Exchange-mandated discrete pricing restrictions create a wedge between the underlying equilibrium price and the observed price. This wedge permits a competitive market maker to realize economic profits that could help recoup fixed costs. The optimal tick size that maximizes the expected profits of the market maker can be equal to $1/8 for reasonable parameter values. The optimal tick size is decreasing in the degree of adverse selection. Discreteness per se can cause time-varying bid-ask spreads, asymmetric commissions, and market breakdowns. Discreteness, which imposes additional transaction costs, reduces the value of private information. Liquidity traders can benefit under certain conditions.]

[We examine the behavior of call options surrounding the underlying stock's ex-dividend date. The evidence is inconsistent with the predictions of a rational exercise policy; a significant fraction of the open interest remains unexercised, resulting in a windfall gain to option writers. This triggers a sophisticated trading scheme that enables short-term traders to receive a significant fraction of the gains. The trading scheme inflates reported volume and distorts its traditional relations to liquidity. The dramatic increases in the volume of trade on the last cum-dividend day are facilitated by limitations on transaction costs passed by the various option exchanges.]

We examine the behavior of call options surrounding the underlying stock's ex-dividend date. The evidence is inconsistent with the predictions of a rational exercise policy; a significant fraction of the open interest remains unexercised, resulting in a windfall gain to option writers. This triggers a sophisticated trading scheme that enables short-term traders to receive a significant fraction of the gains. The trading scheme inflates reported volume and distorts its traditional relations to liquidity. The dramatic increases in the volume of trade on the last cum-dividend day are facilitated by limitations on transaction costs passed by the various option exchanges.