Micellisation of the binary mixture of non-ionic surfactants Triton X100 and Brij S10 is examined. Both surfactants have polyoxyethylene chains of the same length, and differ in the conformational flexibility of the hydrocarbon segment. Triton X100 is the common surfactant in the biochemical laboratories, especially suitable for biological systems since it does not induce protein denaturation, while Brij surfactants show positive effects on the bioavailability of some drugs. According to the regular solution theory (RST), formed binary mixed micelles in each mole fraction of the binary mixture of Brij S10 - Triton X100 are richer in a hydrophobic component (Brij S10), while if the content of the binary mixed micelle is determined using the Rodenas function (the model independent method), then mixed micelles exist that are rich in Brij S10 and mixed micelles rich in Triton X100. According to the experimental values, RST hypothese that the excess entropy is zero cannot be accepted. Also, the dependence of the molar excess Gibbs energy is not a symmetric function. The RST interaction parameter as well as the model independent Gibbs energy show synergistic interactions between Brij S10 and Triton X100. In the infinitely diluted micellar pseudo-phases at T = (283.15-308.15) K the thermodynamic stabilization of Brij S10 and Triton X100 has the entropic origin. (C) 2019 Elsevier Ltd.