There is no real difference between propane gas logs and natural gas log sets. The difference, instead, lies within the combustion source. Propane, which is heavier than air, burns hotter than natural gas. Natural gas, from which propane is derived, is lighter than air. Natural gas is generally less of an explosion hazard than propane. Both types of log sets consist of imitation logs placed over a burner. Upon ignition of the gas burner, the logs will glow and mimic the appearance of a wood burning fire. Propane is a more expensive heat source than natural gas, and there is no noticeable difference between a propane fireplace and a natural gas fireplace.