Utilization of hydrogen (H2)/natural gas (NG) mixtures or pure hydrogen in gas-fired power plants poses a lower carbon footprint instead of the regular 100% NG fuel. Reducing carbon emissions (CO2) in electricity production is fast gaining huge traction in gas power plants, as the attention is shifting from soon eradicated coal power plants to low carbon power plants. Increased interest in the hydrogen economy has further aroused discussions for hydrogen to replace natural gas. This paper evaluates the impact of hydrogen mixtures on existing power plants in three countries: Denmark, Germany, and the United Kingdom. The investigation is carried out using energy, exergy, and economic analysis to depict implications of the various mixtures on each of the power plants. The simulation of the power plants was performed using Ebsilon software, while the calculations of CO2, and NOx emissions were carried out with the aid of the Cantera software and the exergy-based analysis was computed in Excel VBA. The analyzed mixtures of H2/NG presented advantages in all the power plants studied such as lower CO2 emissions, higher energetic and exergetic efficiencies, and, therefore, lower mass flowrates of the fuel mixture. However, NOx discharge, levelized fuel cost (except in the Viborg power plant), and volumetric flowrate increased drastically. Conclusions of this paper will enlighten readers on the technological and economic constraints of using H2-NG mixtures in gas-fired power plants.