Due to the ever increasing proliferation of functional-equivalent web services, the task of finding a proper Web service composition in order to satisfy a set of requirements has become quite challenging. This problem has been typically addressed from the consumer's point of view, assigning the responsibility of discovering the needed services and modeling them as passive entities that wait to be discovered, selected and composed with others. We tackle the service composition problem to satisfy requirements completely from the services' point of view. We propose to wrap services as active software agents, constantly seeking to be selected by consumers and able to formate virtual organizations between them to bid and acquire more complex contracts. We present a Web tool and a simulation component to evaluate our approach with different experiments that characterize the feasibility of the approach in a large market.