How do CDOs work, and what's the difference between cash CDOs and synthetic CDOs?
I'm preparing for FRM and CDOs seem really complex. I understand the basic tranching concept from MBS, but CDOs seem to add layers of complexity. What makes a CDO different from a regular securitization, and why do synthetic CDOs use CDS instead of actual bonds?
A Collateralized Debt Obligation (CDO) is a securitization where the collateral pool consists of debt instruments — corporate bonds, loans, ABS, or even other CDOs. The key difference from basic MBS is the diversity and actively managed nature of the pool.
Cash CDO:
The SPV actually purchases bonds or loans. Cash flows from the portfolio are distributed through a waterfall.
Example — Northgate Capital Management CDO I:
- Portfolio: 100 corporate bonds averaging BB rating, $1B total
- Senior tranche (70%): $700M, rated AAA, SOFR + 60bps
- Mezzanine (20%): $200M, rated BBB, SOFR + 300bps
- Equity (10%): $100M, unrated, targets 15-20% return
Synthetic CDO:
Instead of buying actual bonds, the SPV sells credit protection via credit default swaps (CDS) on a reference portfolio. No physical bonds change hands.
Why Synthetic?
- No need to fund the entire portfolio — much cheaper to set up
- Can reference entities that are hard to buy in the cash market
- The protection buyer (usually a bank) retains the bonds but sheds credit risk
| Feature | Cash CDO | Synthetic CDO |
|---|---|---|
| Collateral | Actual bonds/loans | CDS contracts |
| Funding | Fully funded | Partially or unfunded |
| Setup cost | High | Lower |
| Liquidity of reference | Must be available | Any CDS-able entity |
| Typical use | CLO managers seeking returns | Banks hedging credit portfolios |
Correlation Trading:
The value of CDO tranches depends critically on default correlation among the reference entities:
- Equity tranche holders prefer low correlation — they'd rather face predictable moderate losses than an all-or-nothing bet
- Senior tranche holders prefer low correlation — the chance of clustered defaults hitting their tranche is minimal
- Mezzanine holders are in a complex position — their sensitivity to correlation depends on attachment/detachment points
FRM Exam Focus:
Expect questions on how correlation changes affect tranche values, the difference between cash and synthetic structures, and why CDO-squareds (CDOs of CDOs) amplified losses in 2008.
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