Automatic detection of oscillatory variables in the presence of multiple oscillations is still a challenging problem in the literature, despite the fact that there are several methods for detection and estimation of single-frequency oscillation. A method is proposed that utilizes the autocorrelation function (ACF) to detect the oscillatory variables and estimate the oscillation periods in the presence of multiple oscillations. The advantage of the developed method is that it requires no or little human interference in the detection process. It is also capable of estimation of the decay rate for decaying oscillations and is advantageous over methods based on analyzing the power spectrum for oscillation detection in case of nonsinusoidal oscillations. The proposed method is verified through a case study.