Micellar slug for oil recovery

A process for produceing oil from an oil-bearing subterranean reservoir penetrated by wells, which comprises the steps of:

• (1) injecting into said reservoir through an injection well a micellar slug consisting essentially of a surfactant and an aqueous medium, whihc may contain an inorganic salt, said surfactant containing, as essential constituents,
• (a) at least one internal olefin sulfonate having 10 to 26 carbon atoms;
• and
• (b) 0.1 to 100 parts by weight, based on 100 parts by weight of said internal olefin sulfonate, of at least one ether sulfonate having the general formula:
• R.sup.1 -O-(R.sup.2 O).sub.m -(r.sup.3 O).sub.n OR.sup.4 -SO.sub.3 X (I)
• wherein R.sup.1 represents an alkyl or alkenyl phenyl g roup having 12 to 26 carbon atoms or an alkyl or alkenyl group having 10 to 24 carbon atoms, R R.sup.2 represents C.sub.2 H.sub.4 or C.sub.3 H.sub.6 , R.sup.3 C.sub.2 H.sub.4 or C.sub.3 H.sub.6, R.sup.4 represent C.sub.2 H.sub.4, C.sub.3 H.sub.6, or CH.sub.2 CH(OH)CH.sub.2, n>0, m>
• 0, and n+m=0 to 15, and X represents an alkali metal or an alkaline earth metal;
• said micellar slug containing no lower alcohol as a cosurfactant;
• (2) injecting into said reservoir at least one driving fluid;
• and
• (3) recovering oil from said reservoir through a production well.