Interfacial tension is one of the most important physical properties for high-precision simulations to develop the methods of preventing plugging of pipelines in the oil and natural gas industry. This paper reports experimental data with the pendant drop method for the interfacial tension of a decane + methane + water system at temperatures between 278.2 K to 298.2 K and pressures up to 10 MPa. The data show that in this temperature range the interfacial tension in the decane + methane + water system decreases almost linearly with increasing temperature. The results also show that by increasing the pressure of methane, the interfacial tension decreases from 53.98 mN m-1 to 50.23 mN m-1 at 283.2 K and 52.23 mN m-1 to 49.74 mN m-1 at 288.2 K. The nature of the methane pressure dependence of the interfacial tension changes for pressures above around 2.00 MPa. The interfacial tension decreases with the pressure up to 2.00 MPa, but has no pressure dependence above 2.00 MPa. It may be inferred that the decane/water interface is saturated with methane at pressures around 2.00 MPa and at higher pressure the interfacial tension is no longer affected by the presence of methane.