In this study, engine performance, combustion characteristics and exhaust emissions such as CO2, CO, N-2, O-2, O, H, OH, H-2, H2O and NO of a spark ignition engine fueled with different gaseous fuel types such as propane, methane and hydrogen at stoichiometric condition are examined. A validated combustion model by experiments has been used to demonstrate different fuel types' influences on the engine performance and exhaust products. The acquired results are compared with the data of gasoline combustion. The results indicated that the engine operating with the gaseous fuels has close results to the engine fueled with gasoline in terms of performance characteristics such as power output (PO), indicated mean effective pressure and thermal efficiency. The PO of the engine fueled with propane is able to provide 98.2% of the power of the engine fueled with gasoline. The power reduction percentages of methane- and hydrogen-fueled engines are 10 and 22%. The percentage differences of propane, methane and hydrogen are 1.6, 3 and 29% in terms of TE. However, different gaseous fuel kinds lead to remarkable differences in terms of emission formations. 72% less NO formation is seen in hydrogen combustion compared to gasoline combustion. The propane combustion decreases the CO2 and NO up to 3 and 9%, and increases the CO up to 2%. The methane combustion reduces the CO, CO2 and NO by 23, 21 and 35%.