One of the factors which affects the gas lift performance is specific gravity of a lift gas (or the Molecular weight), which can influence the gas solubility in oil and has a direct effect on the gas lift performance.This research, concentrating on lift gas specific gravity, introduces an easy and inexpensive method for increasing the oil production in gas lifted wells.There are some previous researches which have included the lift gas specific gravity in their modeling, but in none of them, a comprehensive research about the effect of lift gas specific gravity in gas allocation optimization, gas lift stability, economic factors, and some other aspects of gas lift is done.