Energy conservation engineering is one of the more recent engineering disciplines to emerge. It combines knowledge from the fields of physics, math, and chemistry with economic and environmental engineering practices. Energy conservation engineers increase efficiency and further develop renewable sources of energy. The main job of energy conservation engineers is to find the most efficient and sustainable ways to operate buildings and manufacturing processes. They audit the use of energy in those processes and suggest ways to improve the systems. They propose utilizing advanced lighting, better insulation, more efficient heating and cooling properties of buildings. Although they are concerned about obtaining and using energy in the most environmentally friendly ways, their field is not limited strictly to renewable energy like hydro, solar, biomass, or geothermal. Energy conservation engineers are also employed by companies in the oil and natural gas extraction industry.