Collateral and rehypothecation: one security, several owners, and the keystone of the whole plumbing

At the close of this series on the plumbing of the dollar, one mechanism remains to be exposed, the one hiding beneath all the others. Repo, the basis trade, shadow banking, eurodollars and the cross-currency basis all rest on one idea: a security pledged as collateral does not sleep, it immediately goes off to back another loan. This reuse, rehypothecation, turns a finite stock of Treasury bonds into a far larger volume of funding. Collateral is the oil of the financial engine, and its circulation is the keystone of the whole edifice.

Rehypothecation is the right, for whoever receives a security as collateral, to pledge it themselves as collateral for another obligation. A hedge fund hands a Treasury bond to its broker to borrow, the broker reuses that same bond to fund itself with a money market fund, which can in turn mobilise it elsewhere. The security has not changed economic owner, but it now backs several superimposed claims. This is how collateral chains form, through the securities-financing transactions that are repo and securities lending.

Collateral velocity

The reference work is Manmohan Singh’s, at the IMF, who proposed measuring this phenomenon through a velocity, on the model of the velocity of money. Collateral velocity is the ratio of the total volume of collateral received by the major intermediaries to the original collateral supplied by primary holders, hedge funds, pension funds, insurers, official accounts. At the end of 2007, ten to fifteen banks at the core of the global plumbing received close to $10 trillion of collateral, for a velocity on the order of 3. In other words, each unit of source collateral backed on average three obligations. The Fed formalised a close measure, the collateral multiplier, analogous to the money multiplier.

When the lubrication seizes

This circulation is not neutral for overall liquidity. After Lehman’s collapse, two things happened at once: available source collateral fell, and velocity dropped. The combined effect, per the IMF, amounts to a contraction of collateral in circulation on the order of $4 to $5 trillion. Post-crisis regulations, by requiring the big banks to cut leverage and strengthen capital, shrank the balance-sheet space dealers devoted to circulating collateral. Less balance-sheet space, less reuse, less lubrication.

The move is not one-way. As central banks shrank their balance sheets, freeing space at dealers, collateral reuse turned back up. It is the same parameter, intermediaries’ balance-sheet space, that governs repo, the basis trade and the cross-currency basis. Collateral and the bank balance sheet are the two scarce resources around which the whole system turns.

The hidden risk: chains that freeze

Rehypothecation creates liquidity, but it also creates a particular fragility. Along a chain, the same security appears as an asset and as collateral at several points at once. If one link defaults, everyone downstream discovers that their collateral is immobilised or contested. That is what happened in 2008, when broker clients saw their rehypothecated collateral frozen in the bankruptcy, and again in 2011 in the collapse of a broker that had reused client assets. Long chains maximise liquidity in calm times, and destroy it at a stroke in a crisis.

Add a measurement problem, central for this journal. Because the same security is counted in several places, the system’s real leverage is higher than it looks, and hard to reconstruct. Financial-stability statistics often include neither pledged collateral nor its reuse, so the supervisor sees a stock, not the cascade of claims it backs.

The keystone

Everything meets here. Repo is the operation by which collateral circulates. The basis trade stacks several floors of it with leverage. Shadow banking makes it its fuel outside the banks. Eurodollars extend the mechanism to the offshore layer of the dollar. And the cross-currency basis displays its price when access tightens. Beneath each of these markets is the same elementary gesture: a security pledged as collateral, then reused, again and again. The stability of the whole therefore depends on a variable that few dashboards really track, the speed at which a finite stock of Treasury bonds turns into a far larger volume of promises. Making this circulation visible is making measurable the very opacity of the system.

---

Primary sources: International Monetary Fund, Manmohan Singh, “Velocity of Pledged Collateral: Analysis and Implications” (Working Paper 11/256, 2011), “Collateral Reuse and Balance Sheet Space” (WP 17/113, 2017), “Collateral and Financial Plumbing” (Risk Books) and, with Goel, “The Pledged Collateral Market’s Role in Transmission to Short-Term Market Rates” (2019); Singh and Aitken, “The Sizable Role of Rehypothecation in the Shadow Banking System” (2010); Federal Reserve, FEDS Notes, “The Ins and Outs of Collateral Re-use” (2018, Infante, Press, Strauss); Pozsar and Singh, “The Nonbank-Bank Nexus and the Shadow Banking System”. Figures and markers verified one by one.