Control of CO2 emissions is one of the most important problems in the 21st century. It cannot be denied that CO2 emissions regulation will be imposed on each corporation in the future. On the other hand, deregulation about energy trading enabled a corporation to sell energy. Considering energy trading, more efficient energy consumption may be possible. We have studied an agent-based planning system to reduce energy consumptions, called distributed energy management systems (DEMSs). In the DEMSs, CO2 emissions regulation is imposed on each corporate entity, and electrical and thermal energy trading among the entities are allowed. We have proposed an energy trading decision method with the application of the market oriented programming (MOP). In this paper, we state that control of CO2 emission basic unit during the energy trading decision process is an important issue to obtain better solutions. We also propose a CO2 emission basic unit control method for the DEMSs. Computational experiments are performed and show effectiveness of the proposed method.