A surfactant and a surfactant formulation comprising at least one ionic surfactant of the general formula R1—O-(D)n-(B)m-(A)l-XY−M+ where R1 is a linear or branched, saturated or unsaturated, aliphatic and/or aromatic hydrocarbon radical having 8 to 30 carbon atoms, A is ethyleneoxy, B is propyleneoxy, and D is butyleneoxy, l is from 0 to 99, m is from 0 to 99 and n is from 1 to 99, X is an alkyl or alkylene group having 0 to 10 carbon atoms, M+ is a cation, and Y− is selected from the group of sulfate groups, sulfonate groups, carboxylate groups and phosphate groups.