What is the main constituent gas in CNG?

Compressed natural gas (CNG) (methane stored at high pressure) is a fuel that can be used in place of gasoline, Diesel fuel and liquefied petroleum gas (LPG). CNG combustion produces fewer undesirable gases than the aforementioned fuels. In comparison to other fuels, natural gas poses less of a threat in the event of a spill, because it is lighter than air and disperses quickly when released. Biomethane -- refined biogas from anaerobic digestion or landfills -- can be used. CNG is made by compressing natural gas, (which is mainly composed of methane, CH4), to less than 1% of the volume it occupies at standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 20-25 MPa (2,900-3,600 psi), usually in cylindrical or spherical shap Ref:https://en.m.wikipedia.org/wiki/Compressed_natural_gases