Realistic models of power systems involve high-order non-linear differential equations. The application of optimal control theory in optimizing such systems involves a high-order nonlinear 2-point boundary-value problem whose solution is very cumbersome. In this paper the imbedding method of solving a free-end, fixed-time optimal control problem is applied to a sixth-order nonlinear power system. The optimal designs for both open and closed loop plants are presented. The results of this application are compared with those by the hybrid linearization method considered by other authors. The results indicate that the 2 methods follow quite closely.