In this study, effects of using helium, nitrogen, air, carbon dioxide and argon gases as working fluid in a beta-type Stirling engine with rhombic drive mechanism and swept volume of 365 cm(3) on the engine performance characteristics for two different stainless steel and titanium displacer pistons at charge pressures of 1-5 bar were examined. The performance characteristics of manufactured Stirling engine were investigated at 1000 K (+/- 10 K) hot end and 300 K (+/- 5 K) cold end temperatures using a specifically designed electrical heater. Energy and exergy analyses were carried out using temperature, pressure, speed and torque values measured in performance tests. As a result of the exergy analysis, helium gas performed the best in the stainless steel displacer piston at a charge pressure of 4 bar and an engine speed of 550 rpm. Under the said conditions, 0.3726 W/K entropy generation and 195.53 W destroyed exergy were calculated in thermodynamic analysis in the helium working fluid. Furthermore, under the same conditions, helium gas achieved the highest efficiency values of 48.04% for thermal efficiency, 56.54% for exergy efficiency and 69.2% for Carnot efficiency. The lowest exergetic performance was revealed in titanium displacer piston when argon was used as working fluid.