Experimental studies were performed to develop and evaluate emission factors for a gas turbine in an Iranian oil and gas processing plant. The average emission factors were estimated to be 0.389, 0.25, 0.011, 0.241, and 0.028 lb pollutant/MMBtu (pound per million British thermal units) for CO, NO2, SO2, THC, and H2S, respectively. The uncertainty analysis showed that the emission factors had different uncertainties with the highest value for SO2 being 100%, the lowest for NO2 being 10.4%, and between 21-25% for all others. In addition, the results showed that there is less influence of operating practices and the fuel gas composition on average NO2 emissions, while these factors can significantly affect CO and THC emissions. In general, there was good agreement between the measured emission factor and the EPA published value for NO2. However, the differences were high for emission factors of other pollutants, confirming that the uncertainty of published emission factors must be considered to avoid risks of underestimating emissions from combustion devices.