Working Paper 537

The Use of Debt and Equity in Optimal Financial Contracts

Bruce D. Smith
John H. Boyd

Revised July 1, 1996

We consider an environment in which risk-neutral firms must obtain external finance. They have access to two kinds of linear, stochastic investment opportunities. For one, return realizations are costlessly observed by all agents. For the other, return realizations are costlessly observed only by the investing firm; however, they can be (privately) observed by outsiders who bear a fixed verification cost. Thus, the second investment opportunity is subject to a standard costly state verification (CSV) problem of the type considered by Townsend (1979), Gale and Hellwig (1985), or Williamson (1986, 1987).

We examine the optimal allocations of investment between the two kinds of projects, as well as the optimal contract used to finance it. We show that the optimal contractual outcome can be supported by having firms issue appropriate (and determinate) quantities of debt and equity securities to outside investors.

The optimal debt-equity ratio necessarily depends (in part) on the firm’s asset structure. Investments in projects subject to CSV problems are associated (in a sense to be made precise) with the use of debt—as might be expected from the existing CSV literature. Investments in projects with publicly observable returns are associated with the use of external equity.

We examine in detail the relationship between the optimal asset and liability structure of the firm. We also describe conditions under which an increase in the cost of state verification shifts the composition of investment towards projects with observable returns, and reduces the optimal debt-equity ratio. Interestingly, the optimal debt-equity ratio is also shown to depend on factors that are irrelevant to asset allocations.

Finally, a large part of the interest in CSV environments has been due to the fact that they may result in equilibrium credit rationing. Our analysis has strong implications for the possibility of equilibrium credit rationing in more general CSV models.

Published In: Journal of Financial Intermediation (Vol. 8, No. 4, October 1999, pp. 270-316)

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