Optimal placement of oil, gas or water wells is a complex problem that depends on reservoir and fluid properties, well and surface equipment specifications, as well as economic parameters. An optimization approach that enables the evaluation of all these information is presented. A hybrid of the genetic algorithm (GA) forms the basis of the optimisation technique. GA operators such as uniform, single-point, two-point crossover, uniform mutation elitism tournament and fitness scaling were used. An additional operator that employs kriging is proposed. The GA was hybridized with the polytope algorithm, which makes use of the trends in the search space. The hybrid algorithm was tested on a set of mathematical mathematical functions with different characteristics in order to determine the performance sensitivity to CA operators and hybridization. Simple test cases of oil production optimization on 16X16 simulation grids with known optimum well locations were carried out to verify the hybrid GA results. Next, runs were carried out for a 32X32 problem. The locations of a production and injection well were optimized in the case of three existing producers. Exhaustive runs were carried out for these cases to determine the effects of the operators, hybridization and the population size on the performance of the algorithm for well placement problems. Subsequently, the optimum configuration of two injection. wells were determined with two existing producers in the field It was observed that the hybrid algorithm is able to reduce the required number of simulations substantially over simple GA. [S0195-0738(00)00502-1].