Several operational modes can be used in the operation of utility plants for petrochemical plants. For the optimization system of a utility plant to be effective, all the possible operational modes should be taken into account. Moreover, due to the variable fuel cost and electricity cost, the objective function in the optimization system may take different forms depending on the utility management strategy. In this paper, we present a utility optimization system that is based on mixed integer linear programming and considers all possible operational modes and various types of objective functions to maximize the flexibility and the usefulness of the optimization system. The user can conveniently choose a suitable operation mode and a type of the objective function. Results of the optimization can be displayed both numerically and graphically.