ABSTRACT:This paper presents a mathematical model of multiple‐use in natural areas. The model represents a unified system for the assessment of cases where some form of development is proposed for relatively natural areas. The focus of the model system is a benefit‐cost analysis. Provisions for the full consideration of easily measured monetary costs and benefits as well as semitangible benefits accruing from environment‐related activities such as outdoor recreation are contained in the model. Means for incorporating desirability as a measure of aesthetics, uniqueness, and environmental quality into the evaluation are provided. Serveral types of constraints have been imposed on the system to increase model realism. A family of compatibility constraints was designed to limit inter‐use conflicts arising from incompatible activities. A form of the gradient optimization algorithm was utilized to facilitate the evaluation. The model system has application in a wide range of problems frequently encountered in environmental planning and assessment as well as natural resources man