The mathematical expression of the trajectory of injected gas stream at lower velocities in liquid was derived by approximating it as the trajectory of a single rising gas bubble. The experimental time-average images of air stream in water were compared with this trajectory and the trajectory of gas jet of higher velocities derived by Themelis et al., respectively. The experimental results coincided with the Themelis’ equation when the Reynolds number at the orifice is higher than 9000. They agreed with the trajectory of a single gas bubble at the Reynolds number lower than 6000.