Case studies from two Nigerian hydrocarbon processing industries, where gas turbine generators (GTG) were used for power generation were analyzed. The first study analyzed a simple cycle power generation where the GTG produced 25 MW of electricity and three separately fired boilers produced the required process steam. The second study analyzed a combined cycle (cogeneration) where the same GTG that produced 25 MW of electricity also generated 90700 Kg/hr of steam from the turbine exhaust gas. The study shows that cogeneration (combined cycle) satisfied all the electric power and steam requirements of the plant. Simple cycle only satisfied the electric power requirement. Other disadvantages of simple cycle show that over 60% of the generated energy is lost to the environment in form of heat. A loss in production worth over $6,182,400 as a result of failure in a separately fired boiler was calculated. The study concludes that cogeneration must be undertaken with an awareness of energy system expansion, generation costs and the need for industrial energy consumption of a given plant.