[Competition among trading platforms has considerably reduced trading fees in stock markets. We show that this evolution is not necessarily beneficial to investors. Although they increase gains from trade when a trade happens, lower trading costs can induce investors to post limit orders with a smaller execution probability. In this case, gains from trade are realized less frequently and investors can be worse off. Our model has testable implications for the effects of trading fees and their breakdown between liquidity suppliers and liquidity demanders on limit order fill rates and bid-ask spreads.]

We study “Algorithmic Market Makers” (AMs) that use Q-learning algorithms to set prices for a risky asset. We find that while AMs successfully adapt to adverse selection, they struggle to learn competitive pricing strategies. This failure is driven by limited experimentation and noisy feedback regarding the profitability of undercutting a competitor. Consequently, an increase in AMs’ profit volatility tends to result in less competitive market outcomes. These features leave identifiable patterns: for example, AMs earn higher rents in the absence of adverse selection, and their bid-ask spreads respond asymmetrically to symmetric shocks to their costs.

Competition among trading platforms has considerably reduced trading fees in stock markets. We show that this evolution is not necessarily beneficial to investors. Although they increase gains from trade when a trade happens, lower trading costs can induce investors to post limit orders with a smaller execution probability. In this case, gains from trade are realized less frequently and investors can be worse off. Our model has testable implications for the effects of trading fees and their breakdown between liquidity suppliers and liquidity demanders on limit order fill rates and bid-ask spreads.

How do resolution frameworks affect the private restructuring of distressed banks? We model a bank’s shareholders and creditors negotiating a restructuring, under two frictions: asymmetric information about asset quality and externalities on the government. High-quality banks signal themselves by delaying the negotiation, which is socially inefficient. Public policies can improve welfare if they reduce the signaling motive or increase the negotiation surplus. Stricter bail-in rules make debt more information sensitive and increase delays. The bank chooses a capital structure with too little renegotiable debt, giving a new rationale, for example, for Total Loss Absorbing Capacity requirements.

Supervision of multinational banks (MNBs) by national supervisors suffers from coordination failures. We show that supranational supervision solves this problem and decreases the public costs of an MNB’s failure, taking its organizational structure as given. However, the MNB strategically adjusts its structure to supranational supervision. It converts its subsidiary into a branch (or vice versa) to reduce supervisory monitoring. We identify the cases in which this endogenous reaction leads to unintended consequences, such as higher public costs and lower welfare. Current reforms should consider that MNBs adapt their organizational structures to changes in supervision. Received January 9, 2017; editorial decision September 15, 2018 by Editor Philip Strahan.