Diagrams describing equilibria between micellar solutions and the solid phase for mixtures of two anionic surface-active substances (surfactants) with a common anion and different cations are discussed. Solutions with fairly high total surfactant concentrations containing and not containing salt admixtures are considered. The dependence of the temperature of solution on the relative amounts of two surfactants is analyzed with the use of the pseudophase model; the analysis is performed for micellar solution-solid surfactant equilibrium conditions written in aqueous pseudophase composition variables (invoking the concept of the solubility product) and in terms of variables characterizing the composition of mixed micelles. The calculation results obtained for aqueous solutions of sodium and magnesium dodecyl sulfates in the absence of salt admixtures and in the presence of NaCl or MgCl₂ satisfactorily agree with the experimental data.