In this paper, phase equilibrium data of tetrabutylphosphonium bromide (TBPB) + CO2, + N-2 semiclathrate hydrates were measured by employing an isochoric pressure-search method. The experimental temperature, pressure, and mass fraction of TBPB ranged from (282.2 to 292.0) K, from (1.32 to 16.86) MPa, and from (0.050 to 0.600), respectively. The results demonstrated that at a given pressure, the temperature required to form mixed TBPB + CO2, + N-2 hydrates was significantly higher than that required for forming pure Co-2 or N-2 hydrates. In addition, the application of TBPB at 0.371 mass fraction, responding to TBPB center dot 32H(2)O, showed the strongest stabilization effect.