Plumbing of Securities Markets : The Impact of Post-Trade Fees on Trading and Welfare

We analyze how costs related to the "plumbing" (i.e., clearing, settlement, and custody) of securities markets affect market quality and welfare. Our model compares two post-trade fee structures for allocating these costs. One charges a uniform fee for all trades, the other, marginal-cost-based structure a reduced fee for internalized trades (which, both traders being from the same broker, are less costly to process). The fee structure affects quote aggressiveness and (the composition of) trading volume. With marginal-cost-based fees, traders decide which counterparties to target through quote aggressiveness, trading off execution probability against fee. Both fee structures are shown to be inefficient, as they impede welfare-improving trades within and across brokers, respectively