Instantaneous fundamental frequency (IFF) is one of the basic signal parameters of speech signals. Accurate estimation of the IFF of speech signals can be used for speaker recognition system, gender identification and emotion recognition. Various methods for estimation of the IFF of speech signals have been proposed in the literature. In this paper, we propose a new method to estimate IFF of speech signals using the discrete energy separation algorithm (DESA) in the low-frequency region. The Fourier-Bessel (FB) series expansion has been used to filter out the low-frequency region from the speech signal. The reconstructed band-limited signal from the FB coefficients is modeled by using the amplitude and frequency modulated (AM-FM) signal model. Amplitude envelope of the reconstructed band-limited signal is estimated using the DESA. The estimation of amplitude envelope function has been used for detection of glottal closure instants (Gels). Inverse of' time elapsed between two consecutive Gels provides IFF of speech signals. Simulation results of' proposed method have been compared with the IFF computed from reference differenced electroglottograph (EGG) signal. The eMU-Arctic database has been used in this work for validation of the proposed method for IFF determination. It has been observed that the proposed method provides accurate estimation of IFF of speech signals at most of time instants. Key words-Instantaneous fu ndamental fre quency (IFF), Dis crete energy separation algorithm (DESA), Glottal closure instants (Gels), Fo urier-Bessel (FB) series expansion, Amplitude and fr e quency modulated (AM-FM) signal model, Sp eech signal analysis.