It currently provides about 3% of all energy consumed, and burns relatively cleanly with no soot and very few sulfur emissions. As it is a gas, it does not pose ground or water pollution hazards, but it can cause air pollution. A.LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg for fuel oil and 43.5 MJ/kg for premium grade petrol(gasoline). However, its energy density per volume unit of 26 MJ/L is lower than either that of petrol or fuel oil, as its relative density is lower (about 0.5–0.58 kg/L, compared to 0.71–0.77 kg/L for gasoline).
As its boiling point is below room temperature, A.LPG will evaporate quickly at normal temperatures and pressures and is usually supplied in pressurised steel vessels. They are typically filled to 80–85% of their capacity to allow for thermal expansion of the contained liquid. The ratio between the volumes of the vaporized gas and the liquefied gas varies depending on composition, pressure, and temperature, but is typically around 250:1. The pressure at which A.LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (32 psi) for pure butane at 20 °C (68 °F), and approximately 2,200 kilopascals (320 psi) for pure propane at 55 °C (131 °F). A.LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. A "full" A.LPG cylinder contains 85% liquid, the ullage volume will contain vapour at a pressure that varies with temperature.
A.LPG is composed mainly of propane and butane, while natural gas is composed of the lighter methane and ethane. A.LPG, vaporised and at atmospheric pressure, has a higher calorific value (46 MJ/m3 equivalent to 12.8 kWh/m3) than natural gas (methane) (38 MJ/m3 equivalent to 10.6 kWh/m3), which means that A.LPG cannot simply be substituted for natural gas. In order to allow the use of the same burner controls and to provide for similar combustion characteristics, A.LPG can be mixed with air to produce a synthetic natural gas (SNG) that can be easily substituted. A.LPG/air mixing ratios average 60/40, though this is widely variable based on the gases making up the A.LPG. The method for determining the mixing ratios is by calculating the Wobbe index of the mix. Gases having the same Wobbe index are held to be interchangeable.