The present study focuses on experimental techniques to understand the self-excited oscillation characteristics in low-density round for fully developed and turbulent flow conditions, as well as rectangular jets, and study the effects Reynolds number, momentum thickness, density ratio and aspect ratio on self-excited oscillation. Two global modes exist in low-density round jets. The results confirms that oscillations in low-density round jets are axisymmetric irrespective of S and D/θ, and turbulent jets can exhibit self-excited oscillations for S ≤ 0.53. Studies on rectangular low-density jet reveal that the jet transitions from a stable to a self-excited state through subcritical and supercritical Hopf bifurcation. Only supercritical bifurcations are observed during transition when AR ≥ 12. For lower aspect ratios, the type of Hopf bifurcation is dependent on the density ratio. SPOD analysis of low AR rectangular jets (AR ≤6) show that the spatial structure of the oscillation is a symmetric mode. SPOD analysis reveals that the spatial structure of the oscillation in high AR rectangular jets (AR ≥ 12) consists of three modes: a symmetric mode, a flapping mode in the major dimension and a complex mode similar to the ce2 mode in elliptic jets.