The phase equilibria of natural gas hydrate were measured using natural gas distributed in the Korean domestic grid. In addition, the hydrate-phase equilibria in the presence of organic inhibitors of methanol and ethylene glycol at various concentrations and a salt (NaCl) were also investigated at 266.2-290.0 K and 0.99-8.86 MPa depending on the type and the concentration of the inhibitors. Experimental results showed that the hydrate-phase equilibria were shifted to the inhibition region in accordance with the increased inhibitor concentration. In the presence of a constant concentration of NaCl (3.5 wt %), the additional inhibition caused by the salt was found to be the same for either methanol or ethylene glycol at any concentration. Comparison of experimental temperature suppression caused by the addition of an inhibitor (both with and without the presence of NaCl) with the calculated results by two prediction methods showed good agreement except for the high concentrations of methanol and ethylene glycol.