The repurchase agreement (repo), a contract that closely resembles a collateralized loan, is widely used by financial institutions to lend to each other. The repo market is divided into trades that settle on the books of the two large clearing banks (that is, tri-party repo) and trades that do not (that is, bilateral repo). While there are public data about the tri-party repo segment, there is little to no information on the bilateral repo segment. In this post, we update a methodology we developed earlier to estimate the size and composition of collateral posted for bilateral repos, and find that U.S. Treasury securities are the dominant form of collateral for bilateral repos. This new finding implies that the collateral posted for bilateral repos is of higher quality than the collateral posted for tri-party repos.