The oil exploration and drilling processes cause damage to the reservoir that result in decreasing production. Well stimulation processes are performed to repair this damage and restore the oil flow. Among them, matrix acidizing aims to unblock the pores by dissolving the rock, organic or inorganic scale through reaction with the injected acid, causing the dilation of the deeper pores to form long wormholes that provide a path for oil to flow from the reservoir to the production well. In this work, acid microemulsions were developed aiming to improve the stimulation process and reduce the problems caused by using acidic solutions, such as fast reaction with the reservoir rocks. The solvents used as the oil phase were kerosene and Solbrax Eco 175/235, while the aqueous phase consisted of hydrochloric acid (32%) and commercial nonionic surfactants based on ethoxylated lauryl alcohol containing different ethylene oxide units in their chains, and the cosurfactants were propanol and butylglycol. Initially, pseudo-ternary phase diagrams were constructed with the described components to determine the best concentrations of surfactant, cosurfactant, oil phase and aqueous phase to obtain microemulsions. The acidic microfluids prepared were characterized in terms of appearance, stability, particle size, density, viscosity, pH and type of emulsion. The most stable systems were selected for performance testing, where the rock-fluid reaction rate was measured. The results showed that a stable acid microemulsion was formed at room temperature, but not all the hydrochloric acid remained in the microemulsion. The best systems to retard the rock-fluid reaction rate were those containing ethoxylated lauryl alcohol with 1 unit of ethylene oxide.