Energy intensity level of primary energy is the ratio between energy supply and gross domestic product measured at purchasing power parity. Energy intensity is an indication of how much energy is used to produce one unit of economic output. Lower ratio indicates that less energy is used to produce one unit of output. Limitations and exceptions: Energy intensity level is only an imperfect proxy to energy efficiency indicator and it can be affected by a number of factors not necessarily linked to pure efficiency such as climate. Statistical concept and methodology: This indicator is obtained by dividing total primary energy supply over gross domestic product measured in constant 2017 US dollars at purchasing power parity.