Method for recovery of hydrocarbons present in an underground formation by injection of a saline aqueous solution comprising at least one surfactant, by means of a numerical flow simulator including at least one model of the evolution of the interfacial tension between said saline aqueous solution and said hydrocarbons as a function at least of the salinity of said saline aqueous solution comprising at least said surfactant, characterized in that at least the following steps are carried out: A) calibrating said model of the evolution of said interfacial tension between said saline aqueous solution and said hydrocarbons as a function of said salinity as follows: a) determining an optimum salinity value for said saline aqueous solution comprising at least said surfactant, said optimum salinity being such that an emulsion formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant and having a salinity corresponding to said optimum salinity value is a three-phase emulsion; b) preparing a plurality of emulsions formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant, said emulsions having distinct salinity values corresponding at least to said optimum salinity, to two salinity values bounding said optimum salinity within a 5% to 10% limit of said optimum salinity, a zero salinity value and a salinity value corresponding to the water solubility limit of the salts of said saline aqueous solution, and measuring said interfacial tension for each of said emulsions; c) determining said model of said interfacial tension evolution as a function of said salinity by seeking constants of said model of said interfacial tension evolution by minimizing a difference between said model and said measurements of said interfacial tension, said model of said interfacial tension evolution as a function of said salinity having a non-symmetric behaviour with respect to said optimum salinity; B) from at least said flow simulator including said calibrated model of the evolution of said interfacial tension as a function of the salinity of said saline aqueous solution comprising at least one surfactant, determining a scheme for recovery of said hydrocarbons from said underground formation, and recovering said hydrocarbons from said underground formation according to said recovery scheme. A) calibrating said model of the evolution of said interfacial tension between said saline aqueous solution and said hydrocarbons as a function of said salinity as follows: a) determining an optimum salinity value for said saline aqueous solution comprising at least said surfactant, said optimum salinity being such that an emulsion formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant and having a salinity corresponding to said optimum salinity value is a three-phase emulsion; b) preparing a plurality of emulsions formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant, said emulsions having distinct salinity values corresponding at least to said optimum salinity, to two salinity values bounding said optimum salinity within a 5% to 10% limit of said optimum salinity, a zero salinity value and a salinity value corresponding to the water solubility limit of the salts of said saline aqueous solution, and measuring said interfacial tension for each of said emulsions; c) determining said model of said interfacial tension evolution as a function of said salinity by seeking constants of said model of said interfacial tension evolution by minimizing a difference between said model and said measurements of said interfacial tension, said model of said interfacial tension evolution as a function of said salinity having a non-symmetric behaviour with respect to said optimum salinity; a) determining an optimum salinity value for said saline aqueous solution comprising at least said surfactant, said optimum salinity being such that an emulsion formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant and having a salinity corresponding to said optimum salinity value is a three-phase emulsion; b) preparing a plurality of emulsions formed by a sample of said hydrocarbons and a sample of said saline aqueous solution comprising at least said surfactant, said emulsions having distinct salinity values corresponding at least to said optimum salinity, to two salinity values bounding said optimum salinity within a 5% to 10% limit of said optimum salinity, a zero salinity value and a salinity value corresponding to the water solubility limit of the salts of said saline aqueous solution, and measuring said interfacial tension for each of said emulsions; c) determining said model of said interfacial tension evolution as a function of said salinity by seeking constants of said model of said interfacial tension evolution by minimizing a difference between said model and said measurements of said interfacial tension, said model of said interfacial tension evolution as a function of said salinity having a non-symmetric behaviour with respect to said optimum salinity; B) from at least said flow simulator including said calibrated model of the evolution of said interfacial tension as a function of the salinity of said saline aqueous solution comprising at least one surfactant, determining a scheme for recovery of said hydrocarbons from said underground formation, and recovering said hydrocarbons from said underground formation according to said recovery scheme.