Trading Fees and Efficiency in Limit Order Markets

Competition among trading platforms has considerably reduced trading fees in stock markets. We show that this evolution is not necessarily beneficial to investors. Obviously it increases gains from trade when a trade happens. Less obviously, it can induce investors to post limit orders with a smaller execution probability. When this happens, 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. It also provides guidance to interpret the effects of inter-market competition on liquidity