Thomas Keating and Marco Macchiavelli | Currently, Eurodollars and fed funds markets combined trade about $220 billion in funds daily, the vast majority of which with overnight tenor. In this paper, we document several features of these wholesale unsecured dollar funding markets. Using daily confidential data on wholesale unsecured borrowing and reserve balances, we show that foreign banks, which make up most of the trading volumes in these markets, keep around 99% of each additional Eurodollar and 80% of each fed fund borrowed as reserve balances. With these risk-free trades, banks earn the spread between interest on reserves and the borrowing rate. Relative to foreign banks, large domestic institutions borrow less often, but when they do, they keep around 99% of each additional Eurodollar or fed fund raised as reserves. Small domestic banks do not display any correlation between net borrowing and their reserves accumulation. We also discuss how regulatory costs affect trading patterns and interest rate differentials in wholesale dollar funding markets.