Varieties of LPG bought and sold include mixes that are primarily propane (C3H8), primarily butane (C4H10) and, most commonly, mixes including both propane and butane, depending on the season � in winter more propane, in summer more butane. Propylene, butylenes and various other hydrocarbons are usually also present in small concentrations. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg forfuel oil and 43.5 MJ/kg for premium grade petrol (gasoline).[1] However, its energy density per volume unit of 26 MJ/l is lower than either that of petrol or fuel oil.

A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589. In the United States, thiophene or amyl mercaptan are also approved odorants.
LPG is synthesised by refining petroleum or "wet" natural gas, and is almost entirely derived from fossil fuel sources, being manufactured during the refining of petroleum (crude oil), or extracted from petroleum or natural gas streams as they emerge from the ground. It was first produced in 1910 by Dr. Walter Snelling, and the first commercial products appeared in 1912. 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. LPG has a typical specific calorific value of 46.1 MJ/kg compared with 42.5 MJ/kg forfuel oil and 43.5 MJ/kg for premium grade petrol (gasoline).[1] However, its energy density per volume unit of 26 MJ/l is lower than either that of petrol or fuel oil.[citation needed]
LPG evaporates quickly at normal temperatures and pressures and is usually supplied in presurised steel gas cylinders. They are typically filled to between 80% and 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 LPG becomes liquid, called its vapour pressure, likewise varies depending on composition and temperature; for example, it is approximately 220 kilopascals (2.2 bar) for pure butane at 20 °C (68 °F), and approximately 2.2 megapascals (22 bar) (319 psi) for pure propane at 55 °C (131 °F). LPG is heavier than air, unlike natural gas, and thus will flow along floors and tend to settle in low spots, such as basements. There are two main dangers from this. The first is a possible explosion if the mixture of LPG and air is right and if there is an ignition source. The second is suffocation due to LPG displacing air, causing a decrease in oxygen concentration. Fortunately, LPG is not toxic, so there is no danger of poisoning. In addition, odorants are mixed with all LPG so that leaks can be detected more easily.

Varieties of LPG bought and sold include mixes that are primarily propane (C3H8), primarily butane (C4H10) and, most commonly, mixes including both propane and butane, depending on the season � in winter more propane, in summer more butane. Propylene, butylenes and various other hydrocarbons are usually also present in small concentrations.
A powerful odorant, ethanethiol, is added so that leaks can be detected easily. The international standard is EN 589.
South Africa� crude oil refineries produce LPG as a co-product of crude oil distillation. These refineries supply LPG in bulk volumes to gas distributors, such as EPG, countrywide.