China had about a million LNG-fueled trucks on its roads in 2025, according to estimates in Shell's LNG Outlook. Sales in the first half of 2024 alone came to about 109,000, more than double the same period a year earlier, and gas trucks took around 35 percent of heavy-duty truck sales in those months. Those trucks burned roughly 22 million tonnes of LNG in 2024, according to IEEFA estimates.
No other market comes close. That makes China the place where LNG as a truck fuel has been tested at scale, and its swings in sales, tied closely to the price gap between LNG and diesel, show how sensitive the fuel's economics are.
Why trucks use liquid gas
The argument is volume. A diesel gallon equivalent of LNG is 6.06 lb, about 2.75 kg, under the definition used by the US Alternative Fuels Data Center. Liquid methane at its atmospheric boiling point weighs about 422 kg/m³, according to NIST data, against about 199 kg/m³ for CNG at 250 bar and 15 °C. LNG therefore packs a little more than twice as much gas into the same tank volume as the highest-pressure CNG.
A worked example: a truck tank holding 100 diesel gallon equivalents needs 100 × 2.75 kg ≈ 275 kg of LNG. At 422 kg/m³ that is about 650 liters of liquid, before allowing vapor space and insulation. The 100 gallons of diesel it replaces occupy about 380 liters. So LNG needs roughly 1.7 times the volume of diesel for the same energy, against about 3.6 times for the same mass of CNG at 250 bar. For a long-haul tractor, that difference decides whether the fuel fits between the axles.
The trade-offs between the two gas forms are set out in CNG vs LNG. The US Alternative Fuels Data Center puts it plainly: LNG suits Class 7 and 8 trucks that need long range, and CNG suits centrally fueled fleets that stay within a region.
The cryogenic tank on the truck
An LNG fuel tank is a vacuum flask built for a truck chassis. An inner vessel of stainless steel holds the liquid; an outer shell surrounds it, and the space between is evacuated and packed with multilayer insulation. Tanks typically run at a few bar, roughly 3–10 bar depending on the engine they feed. One North American manufacturer's single tanks hold more than 100 diesel gallon equivalents in a cylinder 26 inches across and 108 inches long, close to the length limit for day-cab tractors.
Plumbing on the tank handles two phases. A liquid line draws fuel from the bottom, a vapor line connects to the space above the liquid, and an economizer valve lets the engine take vapor first when tank pressure rises, which uses up boil-off before it can vent. On the way to the engine the liquid passes through a heat exchanger warmed by engine coolant, where it turns back into gas.
Boil-off and hold time
Insulation slows heat leaks but cannot stop them. Heat that reaches the liquid boils some of it, and since the tank is sealed, pressure slowly rises. When it reaches the relief valve setting, gas vents. Hold time is the period a parked truck can sit after filling before that happens. Newer vehicle tanks reach ten days or more; earlier generations managed about seven.
Driving resets the clock, since the engine draws fuel and pressure falls. The problem is trucks that stand still: a long holiday weekend, a breakdown, a depot that parks part of its fleet. If a fleet's vehicles may stand idle for over a week, LNG needs a plan for venting or for running the engines periodically.
LNG that ages in storage
Boil-off also changes what is left in the tank. Methane boils at a lower temperature than ethane or propane, so the vapor that leaves first is almost pure methane, and the remaining liquid slowly becomes richer in heavier hydrocarbons. Engineers call this weathering or ageing. A richer fuel has a lower methane number, a measure of resistance to knock, and spark-ignited engines tuned for lean, methane-rich gas can be pushed toward knock if they are fed LNG that has stood for weeks in a lightly used station tank. Fleets with low throughput sometimes find that the fuel quality problem arrives before the venting problem does.
Temperature matters for a related reason. LNG delivered cold, near −160 °C, holds little pressure; LNG that has warmed in storage is called saturated or warm LNG and holds more. The difference determines whether the truck's own tank pressure can push fuel to the engine.
Two engine families: spark ignition and HPDI
Most LNG trucks use spark-ignited engines, the same family as CNG trucks: stoichiometric combustion with a three-way catalyst, which keeps NOx and particulates low with simple aftertreatment. These engines lose some efficiency against a diesel, especially at part load. They take gas at low pressure, so the tank's own pressure is enough to feed them, and they often prefer warmer, saturated LNG that holds higher tank pressure.
High-pressure direct injection, HPDI, takes the opposite approach. A small diesel pilot is injected first and ignites; natural gas follows, injected at high pressure late in the compression stroke, and burns in a diesel-like flame. The engine keeps the high compression ratio and torque of a diesel. Reaching injection pressure requires a cryogenic pump in the LNG supply, so HPDI works with LNG and not with ordinary CNG tanks. Volvo's FH LNG and FM LNG trucks with 13-liter engines rated at 338 kW, on sale in Europe from 2018, use a fuel system widely reported to be Westport's HPDI 2.0, and Volvo and Westport later formed a joint venture to develop the technology further.
| Spark-ignited LNG | HPDI LNG | |
|---|---|---|
| Combustion | Otto cycle, spark plug | Diesel cycle, diesel pilot |
| Fuel supply | Tank pressure, a few bar | Cryogenic pump to high pressure |
| Aftertreatment | Three-way catalyst | Diesel-type systems |
| Main strength | Simplicity, low NOx | Diesel-like efficiency and torque |
Refueling and road distribution
LNG stations keep the fuel in a vacuum-insulated storage tank, refilled by road tanker, and dispense it through an insulated hose with a liquid line and often a vapor return. Drivers wear a face shield and cryogenic gloves, since the liquid and cold metal cause cold burns. Connectors follow ISO 12617, stations follow ISO 16924 internationally, and in the United States NFPA 52 covers LNG vehicle fuel systems and stations alongside CNG.
A full fill takes a few minutes, comparable to diesel. Some stations also dispense LNG-derived CNG, vaporizing and compressing part of their stock, which lets one tanker delivery serve both fleets. Station tanks have the same boil-off physics as truck tanks, and a station with low turnover warms its stock and loses gas.
The tankers that supply stations are the same type that serve off-grid factories, part of a road network for gas described on the page about virtual pipelines. Where LNG comes from small plants at remote fields, the supply chain overlaps with the options for stranded gas.
Europe, North America and bio-LNG
Europe's LNG truck market is far smaller than China's and built mainly along the main freight corridors, with spark-ignited trucks from several manufacturers and HPDI from Volvo. In North America LNG has stayed a niche: a 2009 count found about 3,200 LNG vehicles in the United States against more than 114,000 on CNG, and CNG remains the usual gas fuel for heavy fleets there.
Bio-LNG has given the fuel a second argument in Europe. Biomethane from digesters or landfills, upgraded and liquefied, runs in the same tanks and engines, and some fleets buy it to cut life-cycle emissions sharply. The production side is explained on the page about renewable natural gas. Methane slip at the engine and venting at stations still count against that gain, which is one reason hold time and boil-off management get so much attention in LNG fleets.
