The cooperation knowledge level is a new computer level specifically for multi-agent problem solvers which describes rich and explicit models of common social phenomena. A cooperation level description (called joint responsibility) is developed to describe how participants should behave during interactions in which groups of agents collaborate to solve a common problem. The utility of this model is highlighted in the real-world environment of electricity transport management in which agents have to make decisions using partial, imprecise views of the system and cope with the inherent dynamics of the environment. In such situations the tracking of social action becomes a primary consideration; joint responsibility provides evaluation criteria and the causal link to behaviour upon which such assessment can be based.