Kirkuk gas turbine power plant is supplied by the gaseous fuel from north gas company. The results showed that the theoretical efficiency of the unit is a function for two parameters; the compressor input temperature and the pressure ratio rp . So, the pressure rp ratio depends directly on the compressor input temperature. If the net work of the unit Wnet (Wt - Wc) is taken to be an index for the performance, the efficiency ƞ will be more in summer than that in winter because of the considerable reduction in compressor work Wc , while if the specific energy produced (or consumed specific fuel SFC) is taken as an index for the performance; the actual efficiency ƞac is more in winter since the specific energy produced in winter is greater approaching (4.5 kW.hr.m-3), while it did not exceed (2.8 kW.hr.m-3) in summer, this belong to the performance improving as the load increases approaching the design load, this is prevailing on the power plant operated by the diesel, heavy fuel or crude oil.