Bottled gas is a flammable fuel, usually propane or butane, that has been compressed into liquid form and stored in a portable steel or aluminum cylinder. When you open the valve, the liquid rapidly vaporizes back into gas, which you can then burn for cooking, heating, or powering appliances. It’s one of the most common energy sources for homes without a natural gas connection, for outdoor grills, camping stoves, and a wide range of commercial and industrial equipment.
What’s Actually Inside the Bottle
The gas inside is technically called liquefied petroleum gas, or LPG. It’s a byproduct of oil refining and natural gas processing. The two main types are propane and butane, both of which are hydrocarbons. Propane has three carbon atoms per molecule, while butane has four. In its natural state, LPG is colorless and odorless, so a chemical called ethyl mercaptan is added to give it that distinctive rotten-egg smell. This is purely a safety feature: if gas leaks from a bottle or a connection, you’ll smell it immediately.
Commercial propane sold in bottles must contain at least 90% propane, with the remaining fraction made up of small amounts of butane and other gases. When stored under pressure of roughly 150 pounds per square inch (about twice the pressure in an inflated truck tire), propane stays liquid and packs 270 times more energy than the same volume of propane in gas form. That’s why a relatively small cylinder can fuel a barbecue or a space heater for hours.
Propane vs. Butane
The practical difference between propane and butane comes down to cold weather. Propane boils at -42°C (-44°F), meaning it continues to vaporize and flow as usable gas in extremely cold conditions. Butane boils at -0.4°C (about 31°F). If the temperature drops to freezing, a butane cylinder simply stops working because the liquid inside can’t vaporize. No vaporization means no gas comes out.
This is why propane is the standard choice for outdoor storage tanks, home heating, and any application in cooler climates. Butane tends to be used in portable camping stoves, handheld torches, and cigarette lighters, where it’s typically used in mild weather or indoors. In warmer countries, butane is more common for household cooking because it’s slightly cheaper and works fine year-round where temperatures stay above freezing.
Common Uses
- Home heating and cooking: Millions of rural homes rely on large propane tanks (ranging from 15 kg to 45 kg cylinders, or bulk tanks holding hundreds of gallons) for furnaces, water heaters, and stoves.
- Grilling and outdoor cooking: The familiar 20-pound (9 kg) cylinder attached to a backyard grill is the most recognizable form of bottled gas in North America.
- Camping and portable stoves: Small butane or propane canisters, sometimes weighing just a few pounds, fuel portable cooking setups.
- Vehicle fuel: Propane powers fleet vehicles like forklifts, buses, and delivery vans. It has a higher octane rating than gasoline, making engines more resistant to knocking, though it delivers fewer BTUs per gallon, so vehicles use more fuel by volume.
- Agriculture and industry: Crop drying, greenhouse heating, welding, and powering equipment in areas without grid access.
How Cylinders and Regulators Work
Gas cylinders are made from seamless steel, welded steel, or aluminum, and are rated for service pressures starting at 150 psig and going much higher for specialized uses. Composite cylinders, which use a mix of materials to reduce weight, are designed for a minimum service life of 15 years. The cylinder keeps the gas under enough pressure to remain liquid. When you open the valve, the drop in pressure causes the liquid to boil and become gas, which travels through a hose to your appliance.
Between the cylinder and the appliance sits a regulator. This device drops the high pressure inside the tank down to a safe, consistent level the appliance can use. For butane appliances, the standard delivery pressure is 28 millibar. For propane, it’s 37 millibar. These are called low-pressure regulators and are what most household appliances need. High-pressure regulators, which can deliver 500 millibar or more, exist for specialized tools like industrial torches.
Using the wrong regulator for your gas type or appliance is a genuine safety hazard. Propane and butane regulators are not interchangeable, and the fittings are deliberately designed differently to prevent mix-ups.
Storing Bottles Safely
Gas cylinders should always be stored upright in a well-ventilated area. OSHA standards require that cylinders kept indoors be stored in a dry, well-protected location at least 20 feet (6.1 meters) away from highly combustible materials like oil or solvents. They should never be kept in unventilated enclosures like lockers, cupboards, or sealed sheds. Outdoors, bottles should sit on a flat, stable surface where they won’t be knocked over, and away from heat sources or direct flame.
Because LPG is heavier than air, any leaked gas sinks to the lowest point in a room, like a basement floor or a pit. This is why ventilation matters so much. A gas pocket forming near the ground can ignite from a pilot light, a spark, or even a light switch. The ethyl mercaptan odorant helps, but relying solely on smell isn’t enough in every situation: some people have a reduced sense of smell, and in rare cases the odorant can fade over time in older tanks.
Environmental Footprint
Bottled gas burns cleaner than many other fossil fuels. Propane produces about 12.68 pounds of carbon dioxide per gallon burned. By comparison, diesel and home heating oil produce 22.45 pounds per gallon, nearly 80% more. Propane also doesn’t contaminate soil or water if it leaks, since it vaporizes into the atmosphere rather than pooling as a liquid. This makes it a lower-risk fuel around wells, waterways, and agricultural land.
That said, it’s still a fossil fuel. It produces less CO₂ per unit of energy than coal or oil, but more than natural gas piped directly from a utility. For most people choosing bottled gas, the comparison that matters is against heating oil or electric resistance heating in areas without a natural gas hookup, and in that matchup, propane generally comes out ahead on both cost and emissions.