Due to fast rising energy demand, Southeast Asia has become a larger energy consumer and bigger player in global energy markets. Energy security and environmental emissions reduction have become higher priorities to ensure energy supply at affordable costs, for continued economic growth and development. To address these issues renewable energy plays a vital role in the long-term future for sustainable development. This paper estimates and analyzes the renewable energy potential in the energy mix in two Southeast Asian countries, Indonesia and Thailand. The LEAP energy model is used to develop different renewable energy policy scenarios from base year 2010 to 2050. The results of the simulation show that a large proportion of electricity must be produced by renewables by 2050 if full potential of renewables is to be exploited. In this case, 81% and 88% of CO2 emissions are reduced in Indonesia and Thailand respectively. In implementing renewables at large scale in both these countries the cost of production increases substantially. (C) 2015 Elsevier Ltd. All rights reserved.