Indeed, so-called “repo” activity – that is, the sale of a US Treasury obligation that the seller promises to buy back later at a slightly higher price – has declined considerably, with the balance of such transactions having fallen from $5 trillion before the crisis to $2.5 trillion today. Both the two-year and five-year US repo rates have been pushed periodically into negative territory, owing to the combined effects of risk-averse behavior, investor deleveraging, and stricter banking regulation.