value. The reasoning for tax bills is analogous. Kenneth Garbade presents evi- dence that quarter-end and tax bills trade at lower yields and higher prices relative to nearby bills suggesting the convenience value is priced.20 While possessing no special payment dates, deliverable bills appear also to have special value. Deliverable bills are those that are deliverable against the Treasury bill futures contract on the IMM. The underlying instrument of the Treasury bill futures contract is a 3-month (13-week) Treasury bill with a face value of $1 million. The short or seller of this contract agrees to deliver to the buyer at the settlement date a Treasury bill with 13 weeks remaining to maturity and a face value of $1 million. The Treasury bill delivered can be newly issued or seasoned (e.g., a 26- week bill that has 13-weeks remaining to maturity on the contracts set- tlement date). Deliverable bills are usually expensive to the Treasury bill curve prior to the settlement of the futures contract against which it is deliverable.     19See, Paul Bennett, Kenneth Garbade, and John Kambhu, "Enhancing the Liquidity of U.S. Treasury Securities in an Era of Surpluses," FRBNY Economic Policy Re- view, forthcoming. 20See Garbade, Fixed Income Analytics. Garbade finds that "month-end" bills trade cheap to the bill curve but the effect is much smaller.   CHAPTER4 AgencyInstruments   .S. government agency securities can be classified by the type of issuer-those issued by federal agencies and those issued by govern- ment sponsored enterprises. Moreover, U.S. government agencies that provide credit for the housing market issue two types of securities: deben- tures and mortgage-backed/asset-backed securities. Our focus in this chapter is on debentures. We discuss short-term mortgage-backed securi- ties and asset-backed securities in Chapters 9 and 10, respectively. Federal agencies are fully owned by the U.S. government and have been authorized to issue securities directly in the marketplace. They include the Export-Import Bank of the United States, the Tennessee Valley Authority (TVA), the Commodity Credit Corporation, the Farmers Housing Adminis- tration, the General Services Administration, the Government National Mortgage Association, the Maritime Administration, the Private Export