This question comes up quite a bit and is actually pretty simple. Gas fireplaces use whatever kind of gas is normally used and lined into the home. This can be either natural gas or propane. There is no need to use a special kind of gas. When purchasing a gas fireplace and log system, however, be sure to check if the logs you are purchasing have a special requirement. While most log units can work with either natural gas or propane, there are still some that require one or the other.