In this paper we describe an efficient approach for designing a multi-agent system consisting of mobile robots that cooperate to achieve specific objectives. More specifically we design a cooperative mobile robot system playing a soccer game. Usually it is difficult to design controllers for multi-agent systems without comprehensive knowledge about the system. One of the ways to overcome this limitation is to implement an evolutionary approach to design controllers. This paper introduces the use of a modified genetic algorithm to design controllers for the mobile robots and discover rules that govern emergent cooperative behavior. A model consisting of movable agents in a cellular space is introduced. An experiment and simulations are performed to verify the proposed idea. The experiment and simulation results indicate that, given the complexity of the problem, an evolutionary approach to find an appropriate controller and rules seems to be promising. The implications of the results are discussed.