The majority of the countries use oil as the main source of their energetic matrices. Techniques of Enhanced Oil Recovery (EOR) have been widely used with the aim of increasing oil and gas recovery trapped in oil reservoir, as 011 as improving the sweep and displacement efficiency. The use of tertiary (or advanced) recovery techniques such as Water Alternating Gas (WAG) injection has been considered promising to attend the expectations of improving the oil recovery, at the same it contributes with changes in some chemical properties of the reservoir that facilitate its exploitation. This paper describes the optimization of a water alternating gas injection strategy in an oil reservoir taking into account techniques of Evolutionary Computing used for maximizing the Net Present Value (NPV) of the field in analysis. It was created a program, developed in JAVA, that performs the optimization through the use of the custom evolutionary algorithm implemented and also uses the commercial software GEM®, which executes the numerical simulation and deliver important data to the optimizer.