Due to the decrease of both world oil and gas prices and Southeast Asian proven reserves of hydrocarbons, ASEAN’s energy landscape is undergoing a period of profound change accelerating the energy transition experienced by its member states. Being the 5th largest economy in the world, ASEAN and its over 650 million inhabitants are experiencing considerable energy and environmental challenges and have set interesting targets to achieve. The structural heterogeneity of ASEAN explains the contrastive response of its members in managing the energy transition, as well as the various strategies and methodologies adopted to face the energy and de facto environmental challenges. In its own way, the Sultanate of Brunei Darussalam has run genuine energy policies since the emergence of its gas and oil rentier economy in mid-1960s—a pattern that can no longer be sustained. For more than one historical and economic reasons, the case of Brunei Darussalam will be here a revealing case study.