We study supply‐and‐demand effects in the U.S. Treasury bill market by comparing the returns on T‐bills to the policy rate on the Federal Reserve's reverse repurchase (RRP) facility. We develop and test a simple model where the RRP‐bill spread is policed both by heterogeneously elastic money funds and by corporate treasurers who derive collateral benefits from holding T‐bills. In response to shifts in T‐bill supply, money funds act as front‐line arbitrageurs. However, when T‐bills become extremely scarce, less elastic corporate treasurers become the marginal investors and supply shifts have a larger effect on T‐bill rates.

Using an experiment in which 3.1 million bank customers were encouraged to save, we explore the mechanisms behind coholding liquid savings and credit card debt. Theoretically, we show that the joint responses of spending, saving, and borrowing to the nudge differ across economic models of coholding. Using machine learning techniques, we find that the most responsive individuals reduce spending and increase savings by 4.9% (206 USD PPP per month) while their credit card debt remains unchanged. These individuals' marginal responses to the nudge are consistent with our model of coholding for the purpose of self‐ or partner‐control.

Although algorithmic trading now dominates financial markets, some exchanges continue to use human floor traders. On March 23, 2020 the NYSE suspended floor trading because of COVID‐19. Using a difference‐in‐differences analysis around the closure of the floor, we find that floor traders are important contributors to market quality. The suspension of floor trading leads to higher spreads and larger pricing errors for treated stocks relative to control stocks. To explore the mechanism, we exploit two partial floor reopenings that have different characteristics. Our finding suggests that in‐person human interaction facilitates the transfer of valuable information that algorithms lack.