Experimental results for the liquid-liquid interfacial tension of water + branched hydrocarbon binary systems were obtained using the pendant drop method. The branched hydrocarbons included in this study were 2-methylpentane and 3-methylpentane as structural isomers Of C6H14; 2,3-dimethylpentane as isomer Of C7H16; and 2,2,4-trimethylpentane and 2,3.4-trimethylpentane as isomers of C8H18. The temperatures at which the experiments were carried out were 303.15, 313.15, 323.15, 333.15, and 343.15 K. Density values of both saturated liquid phases were also experimentally determined. An experimental apparatus for achieving the liquid-liquid equilibrium with online sampling and density measurement was developed. Density values obtained for both saturated liquid phases follow the expected behavior with temperature: they decrease with increasing temperature, whereas the effect of the structural isomerism on density was mainly observed on the results for the hydrocarbon-rich liquid phase. Also, the interfacial tension values decrease with increasing temperature for a given water + hydrocarbon binary system and as the size of the hydrocarbon increases. Estimated values for the interfacial tension of the systems with the different branched isomers were obtained using a method developed in previous work.