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Category — Bond Types
By Konstantin Vasilev Member of the Board of Directors of Cbonds, Ph.D. in Economics
Updated September 11, 2023

What does CDO mean?

A Collateralized Debt Obligation (CDO) is a financial product that is backed by a pool of loans, bonds, or other assets. It is structured in a way that creates different tranches with varying levels of risk and return. These tranches are then sold to investors. The income generated from the underlying assets, such as mortgage payments from a pool of mortgages, is used to pay the interest and principal to the CDO investors.

CDOs gained significant attention during the financial crisis of 2007-2008 because many CDOs were based on subprime mortgage loans that defaulted at a higher rate than expected. This led to a cascading effect of financial turmoil as the value of these CDOs plummeted and spread risk throughout the financial system.


History of CDOs

Collateralized Debt Obligations (CDOs) emerged as a financial innovation designed to address banks’ need to free up space on their balance sheets for the purpose of taking on more loans. The concept involved two main strategies: firstly, banks could sell their existing loans, creating room on their balance sheets, and secondly, they could generate profits by originating new loans. CDOs were initially a niche product in the early 2000s but rapidly gained widespread adoption within and beyond Wall Street. This expansion created significant employment opportunities, as quantitative analysts and computer programmers were required to model loan valuations that composed CDOs. Additionally, marketing and selling CDOs to investors necessitated hiring salespeople.

However, CDOs, particularly mortgage-backed securities (MBSs), played a pivotal role in the subprime mortgage meltdown of 2007-2008, culminating in the Great Recession. Many of these mortgages were inaccurately valued, and the bundles themselves were often misrated due to inadequate consideration of the creditworthiness of underlying loans. As a result of these factors, CDOs fell out of favor in the aftermath of the recession. Despite this setback, CDOs have seen a resurgence a few years later.

How do CDOs work?

  1. Pooled Assets. Banks compile a list of various types of loans and debt instruments, such as mortgages, car loans, commercial loans, and more, that can be included in the CDO.

  2. Diversified Portfolio. The bank combines these pooled assets to form a diversified portfolio. This portfolio consists of different debt assets, including loans issued to corporations and individuals, corporate bonds, mortgages, and other debt instruments.

  3. Involvement of Investment Banks. An investment bank might be brought in to assist in selling the diversified portfolio to potential investors. Investment banks have expertise in structuring and marketing financial products.

  4. Formation of Tranches. The cash flows generated by the underlying assets are divided into different tranches. Each tranche represents a different level of risk and return. The tranches are categorized based on their risk profile:

    • Super Senior. The safest tranche, with the lowest risk, usually receives the lowest interest rate.

    • Mezzanine. Moderate risk with a slightly higher interest rate.

    • Equity/Toxic Waste. It has the highest risk, but it offers the highest interest rate. This tranche receives payouts after the others.

  5. Selling Tranches to Investors. The tranches are then sold to various types of investors based on their risk appetite. The most senior tranche, considered the safest, might be sold to institutional investors seeking highly-rated instruments. The riskier tranches might be retained by the CDO issuer or sold to other banks and financial institutions.

Benefits and drawbacks of CDOs

CDOs (Collateralized Debt Obligations) have both benefits and drawbacks, contributing to their popularity and role in the subprime mortgage crisis. Here’s a breakdown of these advantages and disadvantages:

Benefits of CDOs

  1. Diversification. One of the key benefits of CDOs is their ability to provide diversification. By pooling various types of debt assets, such as mortgages, loans, and bonds, CDOs allow investors to spread their risk across a range of underlying assets. This diversification can help reduce the impact of a default in a single asset on the overall investment.

  2. Liquidity Transformation. CDOs transform relatively illiquid assets (individual loans) into more liquid assets (CDO tranches). This liquidity transformation is particularly beneficial for banks and financial institutions, as it allows them to free up capital tied to illiquid assets and reinvest it in other lending activities, potentially generating more revenue.

Drawbacks of CDOs

  1. Complexity. CDOs are highly complex financial instruments with intricate structures involving multiple tranches with different levels of risk and return. This complexity makes it challenging for investors, including professionals, to accurately assess the risk and value of the securities, which can lead to mispricing and unexpected losses.

  2. Repayment Risk. CDOs are exposed to repayment risk, especially when the underlying assets are subprime loans or other high-risk debt. If a significant number of borrowers default on their loans, it can lead to lower-than-expected cash flows for the CDO, affecting the payouts to investors.

  3. Transparency and Information Asymmetry. The lack of transparency in some CDOs can make it difficult for investors to understand the quality and characteristics of the underlying assets fully. This can create information asymmetry between issuers and investors, potentially leading to adverse selection and misaligned incentives.

  4. Market Vulnerability. The interconnectedness of financial markets means that problems in one area can quickly spread to others. The subprime mortgage crisis showcased how the vulnerability of CDOs to default risk can have far-reaching implications, triggering a larger financial crisis.

  5. Credit Ratings Reliance. Investors often rely on credit ratings provided by rating agencies to assess the risk of CDOs. However, during the subprime crisis, these ratings were found to be overly optimistic and didn’t accurately reflect the underlying risks, leading to misguided investment decisions.


The role of CDOs in the subprime mortgage crisis

  1. CDO Popularity and Subprime Mortgages. In the early 2000s, CDOs gained popularity, and issuers began using securities backed by subprime mortgages as collateral. The sales of CDOs increased significantly during this period.

  2. Subprime Mortgages Definition. Subprime mortgages are loans given to borrowers with low credit ratings, indicating a higher risk of default. Many of these loans had low or no down payments and often didn’t require proof of income.

  3. Risk Mitigation Tools. Lenders used tools like adjustable-rate mortgages to mitigate the risks associated with subprime mortgages. These mortgages had low initial interest rates that would increase over the life of the loan.

  4. Lack of Regulation and Ratings Agencies. The subprime mortgage market lacked significant government regulation. Ratings agencies rated mortgage-backed securities as low-risk, making them attractive to investors.

  5. CDOs and Mortgage Demand. CDOs increased the demand for subprime mortgage-backed securities, increasing the number of subprime mortgages lenders were willing to sell. Without this demand, lenders would not have issued as many subprime loans.

  6. Housing Bubble and Defaults. Many believed rising real estate prices would bail out investors and borrowers. However, the housing bubble burst, causing home prices to decline sharply. Subprime borrowers found themselves owing more on their mortgages than their homes were worth, leading to high rates of defaults.

  7. CDO Implosion and Financial Crisis. The correction in the housing market triggered a collapse in the CDO market, heavily backed by subprime mortgages. CDOs performed poorly during the subprime meltdown, causing significant losses for financial institutions. This led to some investment banks going bankrupt or requiring government bailouts.

  8. Impact on Global Financial Crisis. The losses from the CDO implosion contributed to the escalation of the global financial crisis, resulting in the Great Recession, affecting various sectors, including housing, stock markets, and other financial institutions.

  9. Ongoing Use of CDOs. Despite their role in the crisis, CDOs are still used in structured finance investing. They serve as tools for risk management and capital optimization, which are essential goals in financial markets.

Creation of CDOs

  1. Asset Selection. Investment banks start by selecting a pool of cash flow-generating assets. These assets can include mortgages, bonds, commercial loans, and other types of debt.

  2. Repackaging. The chosen assets are repackaged into different classes or tranches based on their credit risk levels. These tranches are designed to offer varying levels of risk and return to potential investors.

  3. Tranche Classification. Each tranche represents a different risk profile. The tranches are often categorized as "super senior," "mezzanine," and "equity" (or some similar naming convention) based on their order of priority for receiving payments and the associated risk. Super senior tranches are the least risky and are paid first, while equity tranches are the riskiest and are paid last.

  4. Securitization. The tranches of securities become the investment products offered to investors. These products are typically in the form of bonds. The bonds may be given names that reflect the tranche’s underlying assets or risk profile.

  5. Rating and Sale. Investment banks work with credit rating agencies to assign ratings based on their perceived risk to the different tranches. The highest-rated tranches are often deemed safer investments and are sold to institutional investors seeking stability. The riskier tranches might be purchased by investors seeking higher returns or might even be retained by the originating institution.

  6. Distribution. The tranches are then marketed and distributed to various investors, such as pension funds, insurance companies, hedge funds, and other financial institutions.

  7. Cash Flows. As borrowers make payments on the underlying assets (such as mortgages), these cash flows are collected and distributed to the different tranches in the order of priority. Super senior tranches receive payments first, followed by mezzanine and equity tranches.

Investing in CDOs

Typically, individual retail investors are not able to directly purchase Collateralized Debt Obligations (CDOs). Instead, these financial instruments are acquired by entities such as insurance companies, banks, pension funds, investment managers, investment banks, and hedge funds. These institutions seek to exceed the interest earned from conventional bonds, like Treasury yields, by investing in CDOs. However, this pursuit of higher returns is accompanied by an increased level of risk.

While the elevated risk profile of CDOs might be justified by the potential for enhanced returns in a stable economic environment, it’s important to recognize that the risk of default on the mortgage loans underlying CDOs can escalate significantly during an economic downturn or recession. Consequently, this heightened risk of default can result in losses for investors who hold CDOs in their portfolios.

Differentiation from Similar Products

  1. CDOs and CMO. Collateralized Mortgage Obligation (CMO) is a structured financial product that pools mortgage loans and divides them into tranches with varying risk profiles, as described earlier. On the other hand, Collateralized Debt Obligations (CDOs) encompass a wider range of instruments such as loans (home, student, auto, etc.), corporate bonds, mortgages, and credit card receivables, offering more diversity in portfolio construction.

    CMOs are issued by Real Estate Mortgage Investment Conduits (REMICs), while CDOs are issued by Special Purpose Entities (SPEs) established by banks. These entities are independently capitalized to maintain a high credit rating for CDO issuance. CMOs may have different security classes based on mortgage risk levels, while CDOs feature tranches formed by slicing cash flows from various instruments, usually with at least three classifications.

  2. CDOs and MBS. Mortgage-backed securities (MBS) are an early form of structured products introduced in the 1980s. Both MBS and CDOs share structural similarities, with CDOs being more complex. MBS involve repackaging mortgages into investable instruments, with two primary types: Residential MBS (RMBS) and Commercial MBS (CMBS).

  3. CDOs and ABS. Asset-backed securities (ABS) are akin to MBS but differ in that the pool of assets consists of various debt assets other than mortgages. An asset-backed security (ABS) is an investment vehicle supported by a collection of debt instruments, like corporate debt, auto loans, home equity loans, and credit card debt. Within this category, a collateralized debt obligation (CDO) can be considered an iteration of an ABS, potentially incorporating not only mortgages but also various other asset types.

  4. CLOs and CBOs. Collateralized Loan Obligations (CLOs) and Collateral Bond Obligations (CBOs) are subcategories of CDOs. CLOs are created using bank loans, while CBOs use corporate bonds.


  • What is a synthetic CDO?

  • Are synthetic CDOs still legal?

  • Who invented CDOs?

  • Are CDOs dangerous?

  • How to invest in CDOs?

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