Option-Adjusted Spread Explained: Evaluating Embedded Option Value Across Fixed-Income Securities

By Bennett Dorsey

A practical, rigorous guide to option-adjusted spread analysis, written for readers who need to understand not only how OAS is calculated, but also what it reveals about fixed-income value, risk, and relative performance.

Beginning with the distinction between quoted yield spreads, Z-spreads, and OAS, the book establishes a clear framework for separating credit, liquidity, interest-rate, and embedded-option effects. It then follows the complete valuation process, from mapping contractual cash flows and selecting a reference curve to building discount factors, modeling interest-rate paths, and solving for the spread that reconciles model value with market price.

What the book coversCash-flow and option analysis: Identify calls, puts, prepayments, sinking funds, make-whole provisions, conversion rights, and other exercise features across different securities.Curves and rate models: Build spot and forward curves, bootstrap discount factors, apply market conventions, and understand binomial trees, mean reversion, volatility, and model calibration.Bond valuation: Price straight, callable, and putable bonds while measuring the value of embedded calls and puts through optimal exercise assumptions.OAS calculation: Apply a constant spread across interest-rate paths, handle accrued interest and settlement details, and solve the valuation equation through numerical iteration.Mortgage and structured products: Analyze borrower prepayment behavior, amortization, tranche waterfalls, extension and contraction risk, and cash-flow uncertainty in mortgage-backed and asset-backed securities.Cross-sector applications: Compare callable corporate, municipal, sovereign, agency, and structured securities using a consistent analytical approach.Risk and model governance: Derive effective duration, convexity, key-rate duration, spread duration, option cost, and vega, while testing assumptions, validating prices, and diagnosing model errors.Built around worked examples

Step-by-step illustrations show why a quoted spread can mislead, how a rate tree is constructed, how a callable bond is valued, and how OAS is estimated for mortgage pools and other structured securities. Later chapters connect security-level analysis to portfolio construction, relative-value decisions, credit research, liquidity assessment, and performance attribution.

Suitable for fixed-income analysts, portfolio managers, risk professionals, students, and investment committee members, this book combines mathematical foundations with practical judgment. Its emphasis on assumptions, sensitivities, exercise rules, and limitations helps readers interpret OAS responsibly rather than treat it as a single all-purpose measure of value.

• Format: Paperback
• Language: English
• ISBN: B0HDMQN9V9
• ISBN13: 9798191826233
• Release Date: August 2026
• Publisher: Independently published
• Length: 203 Pages
• Weight: 1.07 lbs.
• Dimensions: 11.0" x 0.5" x 8.5"