We report an assessment of maximum feasible cost-neutral reduction in the environmental impacts of energy demand growth in the city of Manaus, Brazil. Manaus is a rapidly growing city located in the heart of the Amazonian rainforest (1500 km of rainforest in all directions). Owing to its geographical isolation, it is attractive to explore the extent to which modern renewable and energy efficiency technologies can move it towards energy sustainability - or at least significantly reduce or delay the next expansion of its conventional energy supply project - without increasing the net present value (NPV) of the energy scenario from the societal perspective. Our results, based on collection and analysis of new and existing data, show that on a technical fix basis (ie, without political support for broader policy changes for reducing conventional energy use), about a quarter of conventional energy consumption for the year 2002 can be cost-neutrally replaced with efficiency and renewables.