Use of a mixture comprising a surfactant and a cosurfactant in the form of an aqueous solution for flooding underground deposits of hydrocarbons for mobilizing and recovering the hydrocarbons from the underground deposits, the cosurfactant being a substance or a group of substances selected from the following list: an amphiphilic comb polymer having a backbone with two or more side chains attached to the backbone, the side chains differing from one another and/or the side chains differing from the backbone in their amphiphilic character, an amphiphilic polymer having one or more hydrophobic subunits [A2] based on a polyisobutene block, at least 50 mol % of whose polyisobutene macromolecules have terminally arranged double bonds, and one or more hydrophilic subunits [B2], or an amphiphilic polymer having the general structural formula