The effects of variation of process streams' temperatures and flowrates in an operating Natural Gas Fired Thermal Power Plant (NGFTPP) were investigated using Mathematical Modeling approach. The results showed that with an increase in supply temperatures, the total exchanger area increased from 85874.1 m(2) in the base case to 88255.8 m(2), heat input reduced from 528.1 MW to 496.4 MW, condenser duty increased from 284.4 MW to 306.8 MW, the cycle efficiency reduced from 46% to 38.2%. The reduction in inlet temperatures increased the area, heat input and efficiency to 92443.9 m(2), 543.9 MW and 51.8%, respectively. The condenser duty reduced to 262.0 MW. An increase in the flow rates increased the area, heat input, condenser duty to 90699.7 m(2), 530.1 MW and 298.6 MW, respectively. The cycle efficiency was 43.7%. Reduction in flow rates reduced the area, heat input and condenser duty to 81089.9 m(2), 506.1 MW and 270.2 MW, respectively. The cycle efficiency increased to 46.6%. The study concluded that any variation in the process streams parameters affects thermodynamics and economic performances of thermal power plant. (C) 2013 Elsevier Ltd. All rights reserved.