A method is presented for determining the relationships between the costs and technical performance of vapor power systems in a manner which permits fundamental design specifications to be made optimally with respect to overall system lifetime costs. Means of applying optimization techniques for large scale systems to the thermoeconomic analysis of vapor power systems are described and demonstrated with a simplified sample model. The example studied is an environmentally driven ocean thermal gradient system. A sequential unconstrained minimization algorithm is employed for overall system design optimization.