CNG (Compressed Natural Gas) is methane (CH4) and LPG (Liquefied Petroleum Gas) is propane (C3H8) and/or butane. CNG is an abbreviation of “Compressed Natural Gas” whereas LPG is an abbreviation of “Liquefied Petroleum Gas”. The main constituent of CNG is methane gas, whereas the main constituents of LPG are propane, butane and other lighter hydrocarbon gases. CNG and LPG fuel also have both similarities and differences. What's the difference between CNG and LPG? CNG is Compressed Natural Gas, which is mainly methane compressed at a pressure of 200 to 248 bars. CNG is Compressed Natural Gas, which is mainly methane compressed at a pressure of 200.