Abstract: The present invention features a method for determining a performance index for each power-generating system, directly correlated to load demands. This performance index can be easily interpreted by power engineers and operators, so that weak areas and potential voltage collapse conditions can be predicted and corrected. When the underlying cause of collapse is due to load variations, the performance index of the current invention has the ability to assess the amount of load increase that the system can tolerate prior to such collapse. When the underlying collapse mechanism is due to a contingency, the performance index of this invention can measure its severity. The performance index of this invention can also assess whether the system can sustain a contingency without collapse.