Greening the global energy sector implies the development and implementation of large-scale energy projects around the world. The quality and effectiveness of the environmental assessment plays a central role in achieving the declared results of eco-modernization: the ability to comprehensively and quickly assess the current activities of an energy facility or an investment project planned for implementation allows one to quickly implement environmental and management solutions. The energy sector is the largest emitter of greenhouse gases into the atmosphere and the largest consumer of natural resources; this is what one considers in most of the proposed approaches to environmental assessment in the scientific and methodological literature. However, in addition to greenhouse gas emissions (in particular CO2), energy facilities operating on traditional and alternative fuels consume a significant amount of oxygen as a result of their combustion, which also has a number of negative environmental consequences. The purpose of the study is the development of a methodology for rapid environmental assessment of energy projects, taking into account CO2 emissions and oxygen consumption. The article presents specific indicators of oxygen consumption and CO2 emissions per unit of generating capacity for various types of fossil and alternative fuels and their adoption on the example of a biogas project at a regional energy facility.