Realism, accuracy, operating action, and cost of operation are just a few of the reasons gas airsoft guns have become extremely popular in the United States in recent years. The most important aspects of owning, operating, and maintaining a gas airsoft gun is the appropriate selection of propellant. The most commonly used propellants are 134A, green gas, and CO2.

The type of gas needed is determined by several factors. Airsoft guns are typically designed to run only one type of gas. However, there is an inherent problem with this approach. The pressure a gas exerts, power in the case of an airsoft gun, depends on temperature. The same propellant that is acceptable at room temperature may be harmful to the same airsoft gun, in let's say Arizona in August.

The exact opposite also holds true. A gas airsoft gun that works perfectly fine indoors during the winter months in Montreal may begin to malfunction soon after stepping outdoors. In this case because of the decrease in temperature, the gas pressure inside the airsoft gun has dropped to such a level that there is no longer enough power to complete the firing action of the gun. This reduced pressure can also allow the valve to remain open after a shot and result in the expulsion of the remaining gas.

Gas selection depends on the manufacturers initial design intentions, as well as, the temperature at which the airsoft gun will be operating. While using a more powerful gas or using the recommended gas at an elevated temperature you run the risk of damaging your airsoft gun.

134A is typically recommended for airsoft guns of Japanese origin, although there are exceptions. This gas can be used under all but the coldest environmental conditions. The temperature drop during the winter months usually starts affecting these guns at 40 degrees and below. When your airsoft gun begins to misfire it is general safe to move to the more powerful green gas or propane.

Green gas is the most popular of the gases in airsoft. The majority of guns, especially from countries other than Japan, are designed to utilize this type of gas. During summer months, the temperate may cause green gas may become too powerful and damage your gun. The quality of airsoft guns that are designed to use green gas vary greatly, and make a hard temperature limit difficult at best. However, if the ambient temperature is approaching 100 degrees Fahrenheit you may wish to switch to the less powerful 134A. The amount of direct sunlight and frequency of use need to be considered as well, if your airsoft gun is in continuous use, the process of expelling a little gas for each shot will actually lower the temperature of your gun.