Yes - low temperature and/or high pressure are needed, how extreme of either depends on the gas.
because that's what it is?Liquefied Petroleum Gas = LPG
LPG: Liquefied Petroleum Gas CNG: Compressed Natural Gas
gas
by compressing it
NGL is not liquefied natural gas, which is condensed natural gas that is compact and therefore convenient for overseas shipping.
Helium.
You cool it down.
Yes.
That the gas has liquefied.
Carbon dioxide (CO2) can be liquefied under pressure at ordinary temperature.
lpg
sometimes