This paper presents a comparative performance evaluation of SVS auxiliary controllers for transient stability enhancement of long transmission lines. A new controller, namely, the Combined Reactive Power and Frequency (C.R.P.F.) auxiliary controller, has been developed for the SVS located at the middle of the transmission line. The application of auxiliary controllers considerably enhances the system damping, and unstable system modes are stabilized. A digital computer simulation study has been performed to illustrate the comparative effectiveness of the auxiliary controllers under disturbance conditions, and the superiority of the C.R.P.F. auxiliary controller has been established.