A collateralized loan obligation (CLO) is a special-purpose vehicle that owns a portfolio — typically 150 to 400 — of broadly syndicated leveraged loans and pays for that portfolio by issuing its own securities in slices, or tranches. CLOs are the largest single buyer base for leveraged loans, which makes them central plumbing for corporate credit.
The structure is a waterfall. Interest collected from the loan portfolio flows first to the most senior tranche (usually rated AAA), then down through AA, A, BBB, and BB notes, with whatever remains going to the equity tranche at the bottom. Losses run in the opposite direction: equity absorbs the first defaults, and each rated tranche is protected by the capital junior to it — its "subordination" or credit enhancement.
Unlike the static securitizations many associate with the financial crisis, a CLO is actively managed. A collateral manager buys and sells loans within rule-based constraints during a multi-year "reinvestment period," reinvesting principal proceeds into new loans. After reinvestment ends, principal repayments pay down the tranches in order of seniority — unless the deal is "reset" or "refinanced," extending its life or cutting its liability costs.
Structural protections keep the waterfall honest. Overcollateralization (OC) tests compare the par value of the loan pool to the outstanding balance of each tranche; interest coverage (IC) tests compare interest collections to interest owed. If a test fails, cash that would have flowed to junior tranches and equity is diverted to pay down senior notes until the test is back in compliance. Concentration limits cap exposure to single borrowers, industries, CCC-rated loans, and second-lien or cov-lite collateral.
CLO equity is the residual claim: it receives the spread between what the loan pool earns and what the tranches cost, levered roughly ten times. In benign environments, equity distributions are substantial; in default waves, OC test diversions can shut off equity cash flow entirely. Equity holders (often the manager or a dedicated fund) also typically control resets and calls.
Who buys the debt tranches? Banks and insurers dominate the AAA and AA notes, attracted by floating-rate assets with historically negligible default rates at those ratings; asset managers and hedge funds take mezzanine risk. It is standard to note that senior CLO tranches performed well through both the 2008 crisis and 2020 — a track record that is itself part of why the market has grown.
Two adjacent markets share the mechanics. Middle market or "private credit" CLOs securitize direct loans rather than syndicated ones, with higher spreads and thicker equity. And the broader technology — pooling assets, tranching claims — is the subject of our securitization guide.
Terms you will meet in coverage: "arb" (the arbitrage between portfolio yield and liability cost that determines whether new CLOs get created), "warehouse" (the financing line used to accumulate loans before a CLO prices), "reset/refi" (repricing a deal's liabilities), "par build" (buying loans below par to grow OC cushion), and "manager tiering" (the pricing gap between the most and least sought-after collateral managers).