Primary dealers, who are responsible for absorbing any supply not bought by direct or indirect bidders, took 27 percent, the smallest amount since April 2018.

Indirect bidders, who include fund managers and foreign central banks, took 61.71 percent of the supply, lower than 62.25 percent in August and the average of 62.55 percent. Direct bidders took 11.29 percent, higher than the 8.04 percent taken in August, which was the lowest since February.

The ratio of bids to the amount of 30-year debt offered - a measure of overall demand - was 2.34, higher than 2.27 in August but lower than the average of 2.39.

The offering was smaller than the $18 billion auctioned in August, but larger than the average of $13 billion at this maturity.