Motivational concepts, such as approach and avoidance goals, have an increasing impact on cognitive models (Markman et al., 2005). In this paper a concept of a cognitive system of motivation (COSMO) is presented that focuses on goal striving by calculating an optimal investment of resources. As a basis a mathematical model of interaction between agents and environments was developed. The intention is to design a general cognitive system that can be used for a wide range of environments serving as an operator for more specific cognitive systems. A second aim is to predict motivational mechanisms by concentrating on characteristics of biological agents.