In multi-agent environments where agents independently generate and execute plans to satisfy their goals, the resulting plans may sometimes overlap. In this paper, we propose a collaboration mechanism using social law, through which rational agents can smoothly delegate and receive the execution of the overlapping parts of plans in order to reduce the cost of plan execution. Also, we consider col laboration with agents that do not abide by social law, that is, self-centered agents. Simulation results show that our mechanism also has the property of balancing t he cost of plan execution and shows flexibility towards selfcentered agents.