Rock-Fluid assays in order to find the Interfacial tension (IFT) needed for the injection of Surfactants in an Enhanced Recovery Project. Argentina The interest in every Enhanced Oil Recovery Project (EOR) focus on oil production increase on hydrocarbons reservoirs using chemical injection method (CEOR) with polymers (P) and the surfactants-polymers blend (SP). The goal is to develop a complementary methodology that involves the interfacial tension (IFT) required to reduce the Residual Oil Saturation (Sor) through rock-fluid lab test. Setting a Target Sor value less or equal to 10% heading a commercial production and looking forward to determine the Capillary Number (CN) that satisfies it, the experimental protocol consist in water/ oil injection assays in a triaxial cell at reservoir pressure and temperature (Net Overburden Pressure, NOBP), where the displacing fluid velocity is the growing manipulated variable keeping the IFT value constant, with CN and Sor as dependent variables. The CN is defined, once the value of the displacing fluid velocity is found for the Target Sor, though the value of IFT is evaluated, keeping the fluid velocity constant. Thus, is necessary a CN of order 10-2 in order to get Target Sor and therefore a IFT value of order 10-3 dinas/cm (mN/m). This guides the fluid-fluid screening stage to a new horizon, looking forward a surfactant, or blend of them, that reduce the value of the IFT to at least 10-3 mN/m in order to reduce the value of the Sor at least 10% in a lab test