The general aim of our work is to provide tools, methods and models to adaptive multi-agent systems designers. These systems consist in several interacting agents and have to optimize problem solving in a dynamic environment. In this context, the ADELFE method, which is based on a self-organizing adaptive multi-agent system model, was developed. Cooperation is used as a local criterion to self-organize the collective in order to reach functional adequacy with the environment. One key stage during the design process is to instantiate a cooperative agent model that is an extension to classical reactive models in which cooperation subsumes any other nominal behavior. A sample implementation of the agent model in the collective robotics domain – resource transportation – will illustrate a discussion on the model.