The present invention relates to a method for analyzing energy used for producing a unit of mass or volume of compressed gas (Specific Energy Consumption) in relation to a common output flow in a compressor system, said method comprising the following steps: —for time interval, Tref, collecting reference measured data points of common output flow Fref and energy (or power) consumption Eref (or Pref) in the compressor system; —calculating energy (or power) use as a function of the common output flow Eref (F) (or t(F)) from the measured data points and calculating volume output as a function of the common output flow Vref(F): —calculating average energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output flow t(F) from equation Eref(F)/Vref(F) (Or t)/Pref); —for time interval, Tsav, collecting measured data points of common output flow Fsav and energy (or power) consumption Esav (Psav) in the compressor system; —calculating energy consumed for producing a unit of mass or volume of compressed gas as a function of the common output flow t(F) from equation Esav(F)/Vsav (F) (or t(F)/F sav) or SECsav(t,F) from Psav/Fsav; —calculating the difference between t(F) and t(F) or SECsav(t,F) over a range of common output flow F in the compressor system.