Liquefied natural gas, or LNG, starts as ordinary natural gas pulled from underground reservoirs, then gets cooled to roughly −160°C (−260°F) until it becomes a liquid. That cooling shrinks it to about 1/600th of its original volume, making it compact enough to ship across oceans on specialized tankers. The journey from wellhead to your home’s gas line involves extraction, purification, liquefaction, ocean transport, and regasification.
Where the Gas Itself Comes From
Natural gas forms deep underground over millions of years as heat and pressure break down ancient organic material trapped in sedimentary rock. It collects in porous rock formations, often alongside oil deposits, and is extracted through conventional drilling or hydraulic fracturing. The raw gas that comes out of the ground is mostly methane, but it also contains water vapor, carbon dioxide, hydrogen sulfide, mercury, and heavier hydrocarbons like ethane and propane.
Most LNG originates from a handful of gas-rich nations. The United States is currently the world’s largest LNG exporter, surpassing both Australia and Qatar. Other major suppliers include Russia, Malaysia, and several countries in West Africa and the Middle East. Some gas never reaches shore at all: floating LNG (FLNG) vessels sit directly above undersea gas fields, extracting, treating, liquefying, and storing the gas on a single ship before transferring it to carriers.
Cleaning the Gas Before Cooling
Raw natural gas would damage liquefaction equipment and pose safety risks if it weren’t cleaned first. Pre-treatment removes impurities to extremely tight limits. Water vapor must drop below 0.1 parts per million by volume, because even tiny amounts would freeze and clog equipment at cryogenic temperatures. Carbon dioxide is capped at 50 ppm, hydrogen sulfide at 4 ppm, and mercury at near-zero levels. Heavier hydrocarbons like butane and pentane are also separated out, often sold as their own products.
What remains after cleaning is a gas that’s typically 87% to over 99% methane, depending on the source. “Light” LNG sits above 95% methane, while “heavy” LNG dips below 90%, containing more ethane and propane. The exact blend matters because it affects how the fuel burns in engines and power plants.
How Gas Becomes Liquid
Liquefaction is the most energy-intensive step. The cleaned gas passes through massive cryogenic heat exchangers that cool it to about −160°C. At that temperature, methane transitions from gas to liquid. Cooling it further, past −161°C, offers no real advantage.
The dominant technology since the late 1970s is the propane pre-cooled mixed refrigerant process, developed by Air Products and Chemicals Inc. In the first stage, propane refrigeration cools the natural gas down to roughly −40°C. Then a blend of nitrogen, methane, and ethane (in a ratio of about 8%, 46%, and 46%) takes over, chilling the gas the rest of the way in a main cryogenic heat exchanger. The result is a clear, colorless liquid that weighs less than half as much as water.
Shipping LNG Across Oceans
LNG tankers are engineered to keep their cargo at cryogenic temperatures for weeks at sea. Two main designs dominate the global fleet. Moss-type ships use large, independent spherical tanks that sit inside the hull but aren’t structurally attached to it. A moderately sized Moss vessel carries around 140,000 cubic meters of LNG across five tanks. If a tank is breached, the LNG stays contained within the surrounding ship structure.
Membrane-type ships take a different approach: the cargo tank is built directly into the inner hull, which provides structural support. This design allows for larger capacity. The biggest membrane vessels, known as Q-Max ships, hold roughly 260,000 cubic meters of LNG, nearly double the Moss design. Both types rely on heavy insulation to minimize heat gain, though a small amount of LNG constantly evaporates during the voyage. That “boil-off” gas is typically captured and used as fuel for the ship’s engines.
Turning It Back Into Gas
At the destination, LNG arrives at a regasification terminal where it’s warmed back to its gaseous state before entering pipelines. Three main methods handle the heating. Open rack vaporizers run seawater or ambient air over the cold LNG, using natural warmth to do the job. Submerged combustion vaporizers use a flame submerged in a water bath to heat the liquid. Standard heat exchangers transfer warmth from a hot medium, often seawater, to the LNG. Once vaporized, the gas feeds into the same pipeline network that serves homes, factories, and power plants.
Methane Emissions Along the Way
One environmental concern with LNG is methane leaking during production and processing. Methane is a potent greenhouse gas, roughly 80 times more warming than carbon dioxide over a 20-year window, so even small leaks matter. Direct measurements at U.S. liquefaction terminals found that methane emission intensity ranged from 0.007% to 0.045% of the methane in LNG production, a six-fold variation across different surveys and facilities. Those numbers cover only the liquefaction step. Additional methane escapes during extraction, pipeline transport, and shipping, meaning the total supply-chain footprint is larger than any single measurement captures.
Self-reported figures from industry tend to underestimate actual emissions. At two facilities studied by researchers using aircraft-based sensors, measured methane loss was roughly four to eight times higher than what the operators reported to federal regulators. The gap highlights why independent monitoring matters for understanding the true climate cost of LNG.