A comparison of the effectiveness of installing reactive power compensators, such as shunt capacitors, static varcompensators (SVCs), and static synchronous compensators (STATCOMs), was presented in large-scale power networks. A suitablebus was first identified using modal analysis method. The single shunt capacitor, single SVC, and single STATCOM were installedseparately on the most critical bus. The effects of the installation of different devices on power loss reduction, voltage profileimprovement, and voltage stability margin enhancement were examined and compared for 57- and 118-bus transmission systems.The comparative study results show that SVC, and STATCOM are expensive compared to shunt capacitor, yet the effect of installingSTATCOM is better than SVC and the effect of installing SVC is better than that of shunt capacitor in achieving power loss reduction,voltage profile improvement and voltage stability margin enhancement.