The invention relates to the use of a mixture containing a surfactant and a cosurfactant in the form of an aqueous solution for flooding underground hydrocarbon fields in order to mobilise and extract hydrocarbons therefrom, wherein the cosurfactant is embodied in the form of a substance or the group of substances selected from an amphiphilic comb polymer comprising a backbone which is provided with two or more side chains which differ from each other and/or from the backbone in terms of the amphiphilic character thereof, the amphiphilic polymer comprises one or several hydrophobic sub-groups[A2] based on a polyisobutene block and one or several hydrophilic sub-groups[B2], wherein at least 50 Mol % of polyisobutene macromolecules have terminal double bonds and one or several hydrophobic sub-groups [A2] or an amphiphilic polymer of a general structural formula (I).