What Is Methane?

Methane is a colorless, odorless, flammable gas made of one carbon atom bonded to four hydrogen atoms, written CH₄. It’s the simplest hydrocarbon, the first member of the alkane family, and the main component of natural gas. The four hydrogens sit at the corners of a tetrahedron around the carbon, which makes the molecule symmetrical and nonpolar.

What Are Methane’s Properties?

Methane’s physical properties govern how it moves, stores, and changes state. Its chemical properties govern what it takes to make it react at all.

Physical Properties

Methane’s molar mass is 16.04 g/mol against roughly 29 for air, giving it a specific gravity near 0.55. A release indoors rises and pools at ceiling level rather than settling on the floor.

It boils at -161.5°C (-258.7°F) and freezes at -182.5°C (-296.4°F).

A liter of water at room temperature and atmospheric pressure only holds about 22.7 mg of methane. Carbon dioxide manages roughly 60 times that under the same conditions, which is why CO₂ carbonates a drink and methane never could. Water molecules carry a slight electrical charge at each end and methane carries none, so there’s nothing for the water to grip—which is the same reason why oil and water separate. Carbon dioxide is nonpolar too, but it reacts with water to form carbonic acid, which is what lets so much more of it dissolve.

The sulfur smell people associate with a gas leak isn’t methane. That odorant is blended into utility gas downstream, and federal pipeline rules require enough of it that a person with a normal sense of smell can detect gas at one-fifth of its lower explosive limit, which is roughly 1% in air. Cylinder methane from a specialty gas supplier arrives unodorized, since adding a sulfur compound would alter the purity you paid for.

Chemical Properties

Methane is chemically unreactive at ordinary temperatures due to the four carbon-hydrogen bonds holding it together. Breaking the first one takes roughly 439 kJ/mol, which is why methane sits in a cylinder for years without degrading, doesn’t attack the steel around it, and won’t ignite from ambient heat alone.

That same bond strength makes methane the hardest hydrocarbon to oxidize, and it’s the reason chemists have spent decades trying to convert it directly into methanol without much success.

Acids, bases, and most oxidizing agents leave methane alone at room temperature. Oxygen is the exception that matters commercially, releasing about 1,010 Btu per cubic foot in complete combustion. The other one is halogenation: mix methane with chlorine in the dark and nothing happens, but add ultraviolet light and the chlorine substitutes for hydrogen, producing chloromethane and hydrogen chloride. Run it further and you get dichloromethane and chloroform, which is how those solvents are made industrially.

Is Methane the Same Thing as Natural Gas?

Methane and natural gas are not the same thing, though the words get swapped constantly. Natural gas is a mixture that’s mostly methane, with ethane, propane, nitrogen, carbon dioxide, and water vapor accounting for the rest.

How much of the rest depends on the field and the processing. Pipeline specifications commonly set a floor around 90% methane by volume, along with limits on carbon dioxide, sulfur, and moisture.

Natural gas delivered to U.S. consumers averaged 1,036 Btu per cubic foot in 2023, running a few percent above pure methane, according to heat content data from the U.S. Energy Information Administration. The extra energy comes from the ethane and propane still in the stream, which carry 1,770 and 2,516 Btu per cubic foot respectively. Texas averaged 1,018 that year—near the bottom nationally—because its processing plants pull more of those liquids out before the gas reaches the pipeline.

Whether that variation matters depends on what the gas is feeding. Appliances and burners generally run on gas between 950 and 1,100 Btu per cubic foot, and pipelines write heat content limits into their tariffs to keep deliveries in that range. A lab calibrating an analyzer doesn’t have that margin, which is why it buys methane by the cylinder at a stated purity with a certificate of analysis.

What Happens When Methane Burns?

Methane burning completely in air only yields carbon dioxide and water vapor: CH₄ + 2O₂ → CO₂ + 2H₂O. With four hydrogens per carbon, the highest ratio in the alkane family, it produces less carbon dioxide per unit of energy than heavier hydrocarbon fuels.

A methane flame in air reaches roughly 1,950°C (3,542°F). Swap air for pure oxygen and it climbs to around 2,800°C (5,072°F), because there’s no nitrogen soaking up heat. Oxy-acetylene still runs several hundred degrees hotter, which is why cutting torches use acetylene rather than natural gas for most steel work.

The flammable range in air runs from 5% to 15% by volume. Below 5% the mixture is too lean to carry a flame and above 15% there isn’t enough oxygen to sustain one. Autoignition occurs at 537°C (999°F), so a hot enough surface starts combustion with no spark involved.

Starve the flame of air and the reaction stops short, producing carbon monoxide instead of carbon dioxide. On a burner, the visible symptom is yellow tipping on a flame that should be blue.

What Purity Grades Does Methane Come In?

Cylinder methane is sold by purity grade, from around 99.0% at the low end to 99.9995% for research work. Grade names vary between suppliers, so the specification matters more than the label: one company’s ultra high purity methane is 99.99%, another’s is 99.97%.

The impurities are mostly other hydrocarbons, especially ethane, plus nitrogen, oxygen, and moisture. A research purity grade might guarantee ethane under 3 ppm, other hydrocarbons under 1 ppm, and nitrogen under 1 ppm. A 99.0% grade makes no such promise, and for a burner or a combustion rig it doesn’t need to.

The right grade depends on what the impurities would do to your result. Ultra high purity is the usual choice in gas chromatography, where methane runs as an unretained marker for dead time and a stray hydrocarbon shows up as a phantom peak. Calibration mixtures for combustible gas monitors use methane blended to a certified concentration, where blend accuracy matters more than the purity of the base gas. Argon-methane at 90/10, known as P-10, fills gas flow proportional counters for radiation detection, with the methane acting as a quench gas so each pulse terminates cleanly.

How Is Methane Stored and Supplied?

Methane reaches users three ways: compressed in high-pressure steel cylinders, compressed at scale as compressed natural gas (CNG) for vehicle fleets, or chilled into liquefied natural gas (LNG) for bulk transport. Cylinders use a CGA 350 valve outlet, the standard connection for flammable compressed gases.

Methane never sits as a liquid at room temperature. Its critical temperature is -82.6°C (-116.7°F), and above that no amount of pressure will condense it. Propane’s critical temperature is 96.7°C (206°F), which is why a propane cylinder holds liquid and a methane cylinder holds nothing but compressed gas.

That’s also why a methane cylinder’s contents are measured in cubic feet of gas rather than pounds, and why the pressure gauge falls steadily as you draw it down instead of holding until the cylinder is nearly spent.

CNG systems store gas at up to 3,600 psi settled at 21°C (70°F), in tanks rated to handle 125% of that during a fast fill. LNG goes the other direction, chilled to -162°C (-260°F) at near-atmospheric pressure, which shrinks the volume roughly 600-fold and makes long-haul transport by truck and ship practical.

Matching methane to your process means getting both the grade and the format right, and WestAir can help you sort that out.

Lawrence Haynes

Lawrence is the Marketing Director at WestAir Gases & Equipment in San Diego, CA