Energy planning is difficult to model owing to its complex structure, with numerous decision makers, criteria, and scenarios. Fortunately, decisionmaking methods can be helpful for the sustainable development of energy, by the evaluation of different energy sources with regard to multiple aspects, for example, economic, environmental, political etc. In this study, a methodology based on a cumulative belief degree approach is proposed for the prioritization of energy sources. The approach enables the use of all types of evaluations, without the loss of any information. It also allows for incomplete expert evaluations which may occur in the energy sources prioritization problem. Turkey, like many countries, generates most of energy from fossil fuels, which are imported mostly from other countries. However, the enormous increase in oil prices, and an emerging energy demand, owing to economic growth and environmental issues, is forcing Turkey to improve its sustainable energy planning. Therefore, the proposed methodology is applied to the energy sources prioritization of Turkey. Results show that solar power and wind should be considered as the priori sources of energy in Turkey.