The purposes of this paper are to provide a theory of determining the firm's optimal seniority structure of debt and examine the relation between the firm's seniority structure of debt and its characteristics. Unlike previous studies, we develop a theoretical model which explicitly includes the benefits and costs associated with senior debt financing, corporate taxes, risk-aversion in the capital market, and costs of financial distress. We next show how a value-maximized firm searches for the optimal trade-off among the present values of the tax advantage of debt, loss of tax credits, expected costs of financial distress, costs of senior debt financing, and benefit of limited liability. Numerical analysis results show that the firm's value is not only a strictly concave function of its capital structure (with a unique global maximum), but also a strictly concave function of its mix of senior and junior debts (with a unique global maximum). We then show that a firm's optimal seniority structure of debt (i.e. the market value of senior debt divided by the sum of the market values of senior and junior debts) increases for low levels of asset riskiness and decreases when asset riskiness becomes sufficiently great. Our model also suggests that a firm's optimal seniority structure of debt increases for low levels of growth opportunities and decreases for high levels of growth opportunities. We test the predictions of our model on the relation between the firm's seniority structure of debt and its characteristics by using the data for the firms in COMPUSTAT over the 1972 through 1991 time period. The empirical evidence is consistent with our theoretical predictions.
Review of Quantitative Finance and Accounting, Vol.13, No.1, pp.5-28