Liquefied Petroleum Gas (LPG)

What Is Liquefied Petroleum Gas?

Liquefied petroleum gas (LPG) (also called autogas, bottled gas, or propane-butane mix) is a mixture of light hydrocarbon gases, primarily propane (C₃H₈) and butane (C₄H₁₀), that liquefies under moderate pressure of approximately 100 to 200 psi (690 to 1,380 kPa) at ambient temperatures. This property allows LPG to be economically stored and transported in pressurized cylinders, railcars, and tanker ships without requiring cryogenic cooling, making it one of the most versatile hydrocarbon products in global commerce, used as a heating and cooking fuel, vehicle fuel (autogas), and petrochemical feedstock across more than 70 countries.

Key Takeaways

LPG liquefies at moderate pressure without refrigeration, enabling low-cost storage in pressurized steel cylinders and tanks.
Commercial LPG grades range from pure propane (favored in cold climates due to its lower boiling point of -42 degrees Celsius) to butane-heavy blends used in warm regions.
LPG is recovered from two primary sources: natural gas processing plants, which strip propane and butane from wet gas streams, and oil refineries, which produce LPG as a byproduct of crude distillation and fluid catalytic cracking.
The Middle East and North America are the dominant LPG producers, with the United States becoming the world's largest exporter after shale development boosted domestic NGL output.
LPG serves as both an end-use fuel and a petrochemical feedstock, with propane dehydrogenation (PDH) plants converting propane to propylene for polypropylene production.

How Liquefied Petroleum Gas Works

LPG is recovered at natural gas processing plants as part of the natural gas liquids (NGL) extraction process. Wet gas from producing wells contains not only methane but also heavier components including ethane, propane, butane, and natural gasoline. These heavier fractions are separated from the methane stream in a gas plant using refrigeration, lean oil absorption, or cryogenic turboexpander processes. The resulting NGL stream is then fractionated in a series of distillation columns (deethanizer, depropanizer, debutanizer) to isolate individual products. Propane and butane emerge as the LPG fraction and are stored in pressurized spheres or horizontal bullets before pipeline transport to terminal facilities.

The behavior of LPG in a storage vessel is governed by its vapor pressure curve. At 20 degrees Celsius, propane exerts a vapor pressure of approximately 8.4 bar (122 psi) while butane exerts only about 2.1 bar (30 psi). This means commercial LPG composition is adjusted seasonally: propane-heavy blends are sold in winter months and at higher altitudes where temperatures are low enough to prevent butane from remaining liquid and vaporizing adequately at the burner tip. A standard household cylinder in a tropical climate may contain primarily butane, while propane autogas dispensed at a filling station in Canada must be used year-round regardless of outdoor temperature. The cylinder or tank is never filled to 100 percent of volume; a mandatory ullage space of roughly 20 percent is maintained to allow for liquid thermal expansion, preventing vessel over-pressurization as ambient temperature rises.

In vehicle fuel applications (autogas), LPG is supplied from pressurized onboard tanks through a vaporizer-regulator that reduces pressure and converts the liquid to vapor before injection into the engine intake manifold. Autogas produces lower particulate emissions and nitrogen oxide (NOx) levels than gasoline or diesel, and it was the world's third most popular vehicle fuel by fleet size before the expansion of compressed natural gas vehicles. LPG autogas remains especially common in Italy, Turkey, South Korea, and Poland.

Fast Facts: Liquefied Petroleum Gas

Primary components: propane (C₃H₈) and butane (C₄H₁₀), in varying ratios by grade
Boiling point (propane): -42 degrees Celsius (-44 degrees Fahrenheit) at atmospheric pressure
Boiling point (butane): -1 degree Celsius (30 degrees Fahrenheit) at atmospheric pressure
Storage pressure at 20 degrees Celsius: approximately 2 to 8.5 bar depending on mix
Energy content: approximately 46 to 50 MJ/kg (higher than gasoline at 44 MJ/kg)
Global LPG consumption (2024): approximately 320 million tonnes per year
Largest exporter (2024): United States (shale-derived propane/butane)
Largest consumers: China, India, United States, Middle East residential sector

Field Tip:

When gauging an LPG storage vessel, never rely solely on pressure to estimate liquid level. Because LPG vapor pressure is determined almost entirely by temperature rather than liquid volume, the pressure gauge reads nearly constant from 90 percent full to 10 percent full at the same ambient temperature. Use a level gauge, a sight glass, a float gauge, or a weigh scale. Operators who judge LPG inventory by pressure alone routinely run out of product unexpectedly, particularly during rapid consumption periods when tank temperature drops and pressure falls further, masking the actual low-level condition.

LPG as a Petrochemical Feedstock

Beyond fuel use, propane and butane are critical feedstocks for the global petrochemical industry. Propane dehydrogenation (PDH) plants, major examples of which operate in China, the United States, and the Middle East, catalytically remove hydrogen from propane molecules to produce propylene (C₃H₆), the monomer used to manufacture polypropylene plastics, acrylonitrile, and propylene oxide. PDH has expanded rapidly since 2010 as cheap shale-derived U.S. propane exports made the economics attractive for Chinese petrochemical producers who previously relied on naphtha steam crackers to generate propylene as a byproduct. Similarly, butane is used as a feedstock in steam crackers and in the production of butylene and butadiene, which are essential for synthetic rubber (polybutadiene, styrene-butadiene rubber) and the production of methyl tert-butyl ether (MTBE) as a gasoline oxygenate additive.

LPG, NGL, and LNG: Key Distinctions

LPG, natural gas liquids (NGL), and liquefied natural gas (LNG) are frequently confused but represent distinct product streams. NGLs are the broad category of all hydrocarbon liquids extracted from natural gas at processing plants, including ethane, propane, butane, isobutane, and natural gasoline (pentane-plus); LPG is a subset of NGLs covering only the propane and butane fractions. LNG is a cryogenic product composed almost entirely of methane and requires cooling to -162 degrees Celsius for transport, whereas LPG is stored as a liquid under moderate pressure at ambient temperature with no refrigeration required. The handling infrastructure, carrier vessels, storage tanks, and end uses of LPG and LNG are entirely different despite both having "liquefied" in their names.

autogas -- the term used specifically for LPG when sold as a vehicle fuel at filling stations
bottled gas -- a consumer-facing term for LPG sold in portable pressurized cylinders for cooking and heating
propane-butane mix -- a compositional description emphasizing the two primary components
LP gas -- a common abbreviated form used in North American marketing and regulatory contexts

Frequently Asked Questions About Liquefied Petroleum Gas

Why does LPG smell, and is the smell dangerous?

Pure propane and butane are odorless. A sulfur-containing odorant called ethyl mercaptan (ethanethiol) is added at the processing plant at concentrations of approximately 10 to 20 milligrams per cubic metre specifically to give LPG a strong, detectable smell at concentrations well below the lower flammable limit of approximately 1.8 to 2 percent in air for propane. The smell itself is not harmful at these trace concentrations, but it is an emergency signal. If you detect LPG odor indoors, do not operate any electrical switch, open windows for ventilation, evacuate the building, and call the gas supplier from outside. The hazard is not the smell but the potential for a flammable vapor-air mixture to accumulate if a leak is not addressed.

What is the difference between commercial propane and HD-5 propane?

Commercial propane is a broad-specification grade requiring a minimum of 90 percent propane content with no strict limits on propylene (an unsaturated compound that can cause engine deposits). HD-5 (Heavy Duty 5) is a premium specification requiring at least 90 percent propane and a maximum of 5 percent propylene, making it the required grade for vehicle autogas applications and most industrial engine uses in North America. HD-5 propane burns more cleanly in engine combustion chambers and reduces long-term fuel system fouling. In Europe, the LPG vehicle fuel specification is governed by EN 589, which sets its own propylene limits and vapor pressure requirements by climate zone.

How is LPG traded internationally, and who are the main players?

International LPG is traded in very large gas carriers (VLGCs), pressurized or semi-refrigerated tankers with capacities of 75,000 to 90,000 cubic metres, with benchmark cargoes priced against the Mont Belvieu, Texas spot market for propane and butane. Saudi Aramco's CP (Contract Price), published monthly for Saudi Arabian propane and butane, remains the primary pricing reference for Middle East LPG exports to Asia. The U.S. Gulf Coast has become the dominant export origin since 2015, with terminals at Enterprise Products' Houston Ship Channel facilities and Targa Resources' Galena Park handling the bulk of U.S. propane and butane exports. Japan, China, India, and South Korea are the largest import markets, using LPG for residential cooking, petrochemical feedstock, and, in India, the government-subsidized Pradhan Mantri Ujjwala Yojana program distributing LPG cylinders to rural households.

Why Liquefied Petroleum Gas Matters in Oil and Gas

LPG occupies a unique position in the global energy system because it is simultaneously a primary energy fuel, a vehicle fuel, and an industrial feedstock that can be transported to locations entirely without pipeline infrastructure. In emerging markets across sub-Saharan Africa, South Asia, and Southeast Asia, LPG cylinders have displaced biomass (firewood and charcoal) as the primary cooking fuel, delivering measurable public health improvements by reducing indoor air pollution. In oil and gas operations, managing LPG recovery and fractionation efficiency directly affects plant revenue, since propane and butane consistently command higher per-unit margins than pipeline-quality methane. As shale production continues generating surplus NGL output in North America, LPG export infrastructure, pricing dynamics, and petrochemical integration have become defining commercial and strategic considerations for producers, midstream operators, and chemical companies alike.