Wells' latest monthly "Overview, strategy, and outlook" says, "Negative rates on U.S. Treasury bills (T-bills) are already not unusual -- for reasons that are perhaps more technical in nature -- and are discussed in more detail in the 'Strategies for the U.S. government funds' section. We have also seen Treasury repurchase agreement (repo) rates go negative from time to time, though large volumes have not traded at those levels. If the Fed eliminates the IOER, it is possible that we could see negative repo rates become more common, and other rates might follow, moving us from a ZIRP to a NIRP.... `Does it make sense that investors would actually pay to invest money? Ordinarily, one would say no; investors won't assume the counterparty and settlement risk to earn less than zero, but it depends on their alternatives. If the only alternative that maintains a relatively constant value and offers immediate liquidity is a bank deposit for which they are charged a fee, then if the negative rate is cheaper than the fee to the bank, it does make sense."