Method for the production of crude oil from subterranean, oil-bearing formations comprising at least the following steps: Providing an aqueous surfactant composition comprising water and a surfactant mixture, injecting said surfactant composition into the subterranean, oil-bearing formation through at least one injection well, thereby reducing the crude oil-water interfacial tension to less than 0.1 mN/m, and withdrawing crude oil from the formation through at least one production well, wherein the surfactant mixture comprises at least a surfactant having the general formula R 1 -O-(CH 2 CH(R 2)O) a -(CH 2 CH(CH 3)O) b -(CH 2 CH 2 O) c -R 3 -Y - M + and a solubility enhancer having the general formula R 4 -O-(CH 2 CH(CH 3)O) x -(CH 2 CH 2 O) y- R 3 -Y - M +, wherein R 1 is a hydrocarbon moiety having 8 to 36 carbon atoms, R 2 is a hydrocarbon moiety having 2 to 16 carbon atoms, R 3 is selected from the group of • a single bond, • an alkylene group -(CH 2) o -, wherein o is from 1 to 3, • a group -CH 2 -CH -CH 2 -, R 4 is an allyl group H 2 C=CH-CH 2 -, Y - is an anionic group selected from -COO - or -SO 3 -, M + is at least a cation selected from the group of alkali metal ions, NH 4 +, and organic ammonium ions, a is a number from 0 to 69, b is a number from 3 to 70, c is a number from 0 to 50, x is a number from 1 to 69, y is a number from 0 to 50, and wherein • R 3, Y -, and M + in and are identical, • x < b, • y = c, and • the molar proportion of surfactant / solubility enhancer is from 98: 2 to 60: 40. Providing an aqueous surfactant composition comprising water and a surfactant mixture, injecting said surfactant composition into the subterranean, oil-bearing formation through at least one injection well, thereby reducing the crude oil-water interfacial tension to less than 0.1 mN/m, and withdrawing crude oil from the formation through at least one production well, wherein the surfactant mixture comprises at least a surfactant having the general formula R 1 -O-(CH 2 CH(R 2)O) a -(CH 2 CH(CH 3)O) b -(CH 2 CH 2 O) c -R 3 -Y - M + and a solubility enhancer having the general formula R 4 -O-(CH 2 CH(CH 3)O) x -(CH 2 CH 2 O) y- R 3 -Y - M +, wherein R 1 is a hydrocarbon moiety having 8 to 36 carbon atoms, R 2 is a hydrocarbon moiety having 2 to 16 carbon atoms, R 3 is selected from the group of • a single bond, • an alkylene group -(CH 2) o -, wherein o is from 1 to 3, • a group -CH 2 -CH -CH 2 -, R 4 is an allyl group H 2 C=CH-CH 2 -, Y - is an anionic group selected from -COO - or -SO 3 -, M + is at least a cation selected from the group of alkali metal ions, NH 4 +, and organic ammonium ions, a is a number from 0 to 69, b is a number from 3 to 70, c is a number from 0 to 50, x is a number from 1 to 69, y is a number from 0 to 50, and wherein • R 3, Y -, and M + in and are identical, • x < b, • y = c, and • the molar proportion of surfactant / solubility enhancer is from 98: 2 to 60: 40. a surfactant having the general formula R 1 -O-(CH 2 CH(R 2)O) a -(CH 2 CH(CH 3)O) b -(CH 2 CH 2 O) c -R 3 -Y - M + and a solubility enhancer having the general formula R 4 -O-(CH 2 CH(CH 3)O) x -(CH 2 CH 2 O) y- R 3 -Y - M +, R 1 is a hydrocarbon moiety having 8 to 36 carbon atoms, R 2 is a hydrocarbon moiety having 2 to 16 carbon atoms, R 3 is selected from the group of • a single bond, • an alkylene group -(CH 2) o -, wherein o is from 1 to 3, • a group -CH 2 -CH -CH 2 -, • a single bond, • an alkylene group -(CH 2) o -, wherein o is from 1 to 3, • a group -CH 2 -CH -CH 2 -, R 4 is an allyl group H 2 C=CH-CH 2 -, Y - is an anionic group selected from -COO - or -SO 3 -, M + is at least a cation selected from the group of alkali metal ions, NH 4 +, and organic ammonium ions, a is a number from 0 to 69, b is a number from 3 to 70, c is a number from 0 to 50, x is a number from 1 to 69, y is a number from 0 to 50, • R 3, Y -, and M + in and are identical, • x < b, • y = c, and • the molar proportion of surfactant / solubility enhancer is from 98: 2 to 60: 40.