Experiments conducted in axisymmetric low-density jets reveal that the transition to global instability and the frequency selection of the global mode depend on the operating parameters of density ratio, momentum thickness, and Reynolds number. The onset of the global mode was mapped in the Reynolds number–momentum thickness operating domain for density ratios $S \,{=}\, \rho_{j}/\rho_{\infty}$ ranging from 0.14 to 0.5. The results provide convincing evidence of the universality of global oscillations in low-density jets and indicate that conditions in the jet exit plane are responsible for driving the global instability.