ABSTRACT In this paper, we develop a model for valuing debt options that takes into account the changing characteristics of the underlying bond by assuming that the standard deviation of return is proportional to the bond's duration. The resulting model uses the bond price as the single state variable and thus preserves much of the simplicity and robustness of the Black‐Scholes approach. The paper provides comparisons between option prices computed using this model and those using the Black‐Scholes and Brennan and Schwartz models.

In this paper, we develop a model for valuing debt options that takes into account the changing characteristics of the underlying bond by assuming that the standard deviation of return is proportional to the bond's duration. The resulting model uses the bond price as the single state variable and thus preserves much of the simplicity and robustness of the Black-Scholes approach. The paper provides comparisons between option prices computed using this model and those using the Black-Scholes and Brennan and Schwartz models.