Here, we compare the properties of sulfonated methyl esters of fatty acids (SME) and linear alkylbenzene sulfonate (LAS) with respect to the effect of calcium ions on their surface tension and the effect of their mixing on the critical micelle concentration (CMC). The theoretical interpretation of surface tension isotherms obtained in the presence of NaCl and CaCl2 allowed us to determine the parameters that characterize the surfactant adsorption layers and counterion binding. The excluded area per molecule in the adsorption layer is the same for SME and LAS, and is determined by the cross-sectional area of the sulfonate headgroup. The binding energy of Na+ ions to the headgroups of SME and LAS is also the same. However, the binding energy of the Ca2+ ion to the headgroup of LAS is considerably greater than that of SME in agreement with the circumstance that LAS is precipitated by hard water. In contrast, the binding energy of the Ca2+ ion to the headgroup of SME is lower even than that of Na+, in accord with the reputation of SME as one of the most hard-water tolerant surfactants. The dependencies of the CMC on the composition of binary mixed surfactant solutions reveal that C14-SME and C16-SME exhibit ideal mixing; C14-SME and LAS – slightly synergistic mixing, whereas C16-SME and LAS – antagonistic mixing due to hydrocarbon-chain mismatch. The micellization in mixed solutions of SME and cocamidopropyl betaine has been also investigated. The results in the present study allow prediction of the surface tension of solutions of SME and LAS in the presence of Na+ and Ca2+ ions at various concentrations; contribute for a better understanding of the different tolerance of SME and LAS to hard water, and quantify the effect of their mixing on the CMC.