Gas hydrate technology has a great potential for natural gas storage and transportation on the industrial scale. The required water for hydrate formation could be supplied from the sea and river water, in which the dissolved salts inhibit the formation of hydrate. Some additives like tetra-n-butyl ammonium chloride (TBAC), which can form semiclathrate structures, can promote the thermodynamic stability conditions of hydrate formation. Although sufficient phase equilibrium data of TBAC semiclathrate hydrates of methane seem to be available, there are some discrepancies in the phase equilibrium data, particularly for the 0.05, 0.3, and 0.34 mass fractions of TBAC. Furthermore, the phase equilibrium data of TBAC in the presence of NaCl, MgCl2, and mixed NaCl + MgCl2 have not been reported in the literature yet. In this work, first, the hydrate phase equilibrium data of TBAC + CH4 were obtained accurately. In the next phase, the effects of NaCl and/or MgCl2 on the phase stability conditions of TBAC + CH4 hydrate systems were studied. The experiments were conducted with the TBAC aqueous solution at two concentrations of 0.05 and 0.20 mass fractions in the absence and presence of NaCl (0.05 mass fraction), MgCl2 (0.05 mass fraction), and NaCl + MgCl2 (0.05 + 0.05 mass fractions). The phase equilibrium data were reported in the pressure and temperature ranges of (1.27-5.46 MPa) and (282.2-291.8 K), respectively. Equilibrium data show that the presence of NaCl and/or MgCl2 (0.05 mass fraction) + TBAC (0.05 mass fraction) in an aqueous solution has synergetic effects on the promotion of the stability conditions of methane hydrate as compared to that of TBAC (0.05 mass fraction). At a higher concentration of TBAC (0.20 mass fraction), the mineral salts play the role of an inhibitor and shift the methane + TBAC hydrate phase equilibrium curve to the left side. The hydrate dissociation data generated in this work show that TBAC can promote the stability conditions and improve the stability of methane in the presence of the mineral salts effectively.