Although they are usually issued for 3 month (91 days), on occasion they have been issued for 28 days, 63 days and 182 days.
They are issued:
The secondary market in Treasury bills has in recent years become illiquid and representative rates are no longer obtainable other than those for the most recently issued 91 day bills. The rates shown are the average rates of discount at the weekly tender for 91 day bills.
This is the market selling rate in New York for 91-day Treasury bills, expressed as a yield (per cent per annum of 360 days). Figures shown here up to and including 1979 3rd quarter are averages of Friday observations. Thereafter, they are based on daily observations.