This paper proposes a real-time oscillation monitoring system for detecting the emergence of small-signal instability related events in large electric power systems. The oscillation monitoring system has been developed as a fully autonomous expert system for real-time extraction of modal information from the wide-area PMU measurements during the progress of power system disturbance events. The oscillation analysis uses three different algorithms, namely, the classical multiple-input Prony algorithm, the matrix Pencil algorithm as well as the recent Hankel total least square method. These algorithms were primarily used for off-line manual analysis of power system oscillations in the past. In our research, a specific set of rules has been designed to automate the modal analysis of oscillations by using the three algorithms above without any human intervention during the analysis. The monitor will thus issue operator alerts or control triggers whenever the damping levels of the electromechanical modes of oscillation go below preset thresholds.