The selection and the optimal integration of the utility system is a major step of any energy integration study. It allows to determine an energy target based on the cost of the utilities rather than on energy. As a result, we obtain the final list of streams that have to be considered for the Heat Exchanger Network (HEN) synthesis. The technique proposed for calculating the optimal integration of the utilities combines pinch analysis and mathematical techniques. For analyzing the numerical results obtained by the optimization, we propose a new definition of the composite curves (the integrated composite curves) that allows to evaluate the integration of the utility system, including the combined heat and power aspects. The new representation is illustrated on industrial examples. The applications show that it is a powerful tool for understanding the targeting of complex utility systems and for improving their integration to a process or an industrial site.