In the present work, phase equilibrium conditions for tetra-n-butyl ammonium bromide (TBAB) semiclathrate hydrates formed with the gas mixture (29.95 % CH4 + 60.0 % N-2 + 10.05 % O-2 in mole fraction) were measured. The experimental temperature, pressure, and mass fraction of TBAB ranged from (282 to 290) K, from (0.99 to 6.56) MPa, and from (0.05 to 0.20), respectively. For the gas mixture used in this work, the experimental results showed that at a given temperature, the pressure required to form TBAB semiclathrate hydrates is significantly lower than that required for forming gas hydrates from the same gas mixture. The formation pressure of TBAB semiclathrates formed with the gas mixture is reduced as TBAB concentration is increased in the solution at a given temperature.