European trends to get greener cities and protect the environment imply substituting traditional diesel/gasoline engines for gas (gas-hybrid) powered engines. To accomplish this, straightforward quality control of liquefied and/or compressed natural gas is needed. This communication shows that the broadening effect of an auxiliary inert gas (Ar) enhances their infrared (IR) gaseous spectra and improves usual analytical performance parameters by 50%, which paves the way to use IR routinely to assess the composition of natural gas samples.