In combined power-desalting (plants, high available steam (at high pressure and temperature) is expanded first in a steam turbine (and thus produces work) before its extraction (from the turbine) as a heat source to the desalters. The amount of energy consumption charged to the predominantly used multi-stage hash (MSF) desalter in this combined heat and power plant is a question of great concern in the Gulf area. The following are among the methods used to answer this question: (i) the available energy of the heat supplied to the desalter; (ii) work loss from the lower pressure stages of the steam turbine due to steam extracted to the desalter; (iii) energy charged if a separate boiler was used to supply the desalter with its required heat; and (iv) the excess energy supplied to the combined power desalting plant as compared to a single purpose power plant producing the same power output. There would be a different rating method of the power producing process associated with any of the above mentioned charging methods. In this paper, the MSF desalting method and its power consumption are outlined, together with the rating method of the power-desalting plants and the energy charged to the desalter methods. These rating methods are applied to real cases of dual purpose plants Working in Kuwait.