An isochoric equilibrium cell was used for measuring the solid-vapor-liquid equilibrium conditions of semiclathrates formed in an aqueous solution of tetra-n-butylammonium bromide (TBAB). The semiclathrates were formed from two different synthetic landfill gas (LFG) mixtures of CO(2) (1) + CH(4) (2), which had mole fractions of x(1) = 0.4 and x(1) = 0.6. The experimental temperature, pressure, and mass fraction of TBAB ranged from (286 to 293) K, from (3 to 6.5) MPa, and from (0.05 to 0.20), respectively. For both of the gases used in the present study, it was found that, at a given temperature, the pressure required to form semiclathrates is significantly lower than that required for forming gas hydrates from the same gases.