This RMO supplementary comparison aims to assess the analytical capabilities of laboratories for measuring the composition of automotive (or even autogas or vehicle) emissions mixtures composed mainly of carbon monoxide, carbon dioxide and propane in nitrogen (Model 1). The amount-of-substance fractions analysed are relevant for implementing regulations with regard to automotive exhaust gas measurements. A previous Track A key comparison of automotive exhaust gases was recently coordinated by VSL – CCQM-K3.2019 [1], with the participation of INMETRO. Nevertheless, the ranges from the gas mixture components are different from the ones from the Track A comparison. Besides, this present supplementary comparison doesn´t include the component oxygen. For this reason, it was previously arranged this supplementary comparison.