preferred mixture of surfactant a and b comprises a mole ratio of b to a of from about 0 05 to about 0 45 an especially preferred mixture of surfactant a and b comprises a mole ratio of b to a of from about 0 11 to about 0 25 the above example is presented for purposes of illustration only and should not be deemed to limit the spirit of the invention for reservoirs containing brines at different salinities and at different temperatures a different value for the number of moles of ethylene oxide contained in the surfactant may be necessary in many cases it will be advantageous to add so called 34 sacrificial agents 34 these are chemicals which are injected before or with a surfactant solution for the purpose of minimizing surfactant losses to reservoir matrix adsorption effects chemically modified lignosulfonates are often used for this purpose it is anticipated that the most efficient combination of surfactant concentration slug size polymer concentration and type as well as the use of other additives such as sacrificial agents will vary depending on the particular reservoir and conditions encountered generally the surfactant slug will vary in volume from about 0 1 to about 5 0 pore volumes and in.