However, for this strategy to work in oil fields, it would be necessary to employ surfactants able to promote a great lowering of the water/oil interfacial tension values. Most of the studies from the literature [8; 11; 15; 16] that evaluate the performance of surfactant carriers in EOR experiments employ commercial surfactants, such as SDS, which are not able to produce that degree of interfacial tension reduction. For this reason, it was decided to use oleic acid diethanolamide (OADA) as a nonionic surfactant in the present work, since previous results from our group have shown its capacity to lower the water/oil IFT to values inferior to 1.0 mN/m [17]. Polystyrene nanoparticles (PSNP) are gaining interest for application in many different fields, such as reinforcing fillers for polymeric nanocomposites and polymeric films for dielectric utilization [18]. Besides, due to their submicron sizes, they can act as a polymeric delivery system, i.e., drug carriers [19]. One of the most common techniques used for the production of these nanoparticles is the emulsion polymerization reaction, but the size control and suspension stability of the obtained nanoparticles is sometimes difficult to achieve [20]. In this mechanism, the monomer is emulsified with the aid of a surfactant, since it is insoluble in the aqueous phase. For that, the surfactant concentration must be above the critical micelle concentration (CMC). On the other hand, the initiator is water soluble and consequently, the polymerization will start with the few monomer molecules dissolved in the continuous phase. Subsequently, the first oligoradicals formed can be absorbed by micelles containing the monomers, and that gives a continuation to the polymerization process. This mechanism proceeds until monomer/radical depletion occurs, producing 50-300 nm diameter particles [21; 22; 23; 24; 25; 26]. In addition to these factors, [PERSON] and [PERSON]'s study [27] has investigated the influence of higher amounts of initiator and/or surfactants on the final particle size, since the number of particles in the first stage of the reaction is related to the final particle diameter (d \(\propto\) N\({}^{-1/3}\)). Accordingly, experimental conditions, such as emulsifier type and concentration, initiator, monomer chemical structure, stirring conditions and temperature have an influence on the size and other particles' properties. Particle size is an essential parameter in order to ensure that the carrier will be able to permeate through the pores of the reservoir, as would be the stability of the particles aqueous suspensions, since agglomerates could clog the pore throats. To obtain particles smaller than 100 nm and also to prevent nanoparticle agglomeration, sulfonated styrene was employed as a monomer in the present work to obtain partially sulfonated polystyrene nanoparticles (SPSNP). The presence of ionic groups in the polymer structure should increase the nanoparticles suspensions' stability. Their performance as OADA carriers was compared with the one obtained with non-ionic polystyrene nanoparticles (NPPS). Therefore, the main objective of this work was to develop PSNP and SPSNP that would be able to carry oleic acid diethanolamide molecules through reservoirs porous medium and deliver it at the water/oil interface, reducing interfacial tension and increasing oil production.