Glottal Opening Instants (GOIs) are those instants at which the glottis opens from the closed phase of glottal activity. Detecting GOIs leads to parameterization of glottal activity regions in terms of open quotient that may be helpful for speaker verification and speech enhancement tasks. Accurately marking such instants directly from speech signal is still a challenging task. Alternatively, Electroglottograph (EGG) signal provides an accurate means of picking such instants from the voiced activity regions of the speech production. In this paper a detailed procedure of reference marking GOIs manually from EGG signal is reported and then a method is proposed to pick those instants automatically. Eight different subjects are used to create reference markings for selected sentences from CMU-Arctic database of 3 different speakers. The mean average positions obtained from the markings of different subjects within a glottal cycle are used as reference markings to evaluate the automatic procedure. © 2014 IEEE.