The present invention provides an apparatus for performing a process for producing standard gas mixtures which entailspurifying a raw gas using a gas purifier (3) such as a known two stage gas purifier system, thereby generating a high-purity diluent gas;mixing the high diluent gas and at least one high-concentration standard gas, by generating a medium-concentration gas mixture; dividing the medium-concentration gas mixture into a first flow and a second flow;selectively mixing the first flow with a sample gas or a high-purity diluent gas or a mixture thereof, thereby obtaining a standard low-concentration gas mixture; andcontrolling the pressure of the sample gas, the second flow of the medium-concentration gas mixture and the standard low concentration gas mixture.