An apparatus for sampling exhaust gases, in particular from internal combustion engines of motor vehicles, by means of a dilution air system, in which exhaust gas is mixed with dilution air, wherein the apparatus is a constant volume sampling system, comprising: - a tunnel which has fluid passing through it, the tunnel being a dilution tunnel, - a gas conveying means for generating a fluid flow in the tunnel, - an exhaust gas inlet for supplying exhaust gas, and - a venturi nozzle which is used with critical flow, for setting a constant total volume flow, wherein the constant total volume flow results from the addition of the volume flow of the dilution air and the volume flow of the exhaust gas, wherein a measuring point, for determining the volumetric flow rate of the dilution air which is supplied, is provided upstream of the exhaust gas inlet, and a determining means is provided, which is adapted to determine the exhaust gas quantity supplied from the constant total volume which is kept constant by the Venturi nozzle minus the dilution air flow which is supplied and which is determined at the measuring point, wherein the venturi nozzle is arranged upstream of the gas conveying means, and a first flow element is arranged upstream of the venturi nozzle and upstream of the exhaust gas inlet at the measuring point, and wherein the measuring point comprises pressure sensors (P1, P2) for determining the differential pressure upstream and downstream of the first flow element. the apparatus is a constant volume sampling system, comprising: - a tunnel which has fluid passing through it, the tunnel being a dilution tunnel, - a gas conveying means for generating a fluid flow in the tunnel, - an exhaust gas inlet for supplying exhaust gas, and - a venturi nozzle which is used with critical flow, for setting a constant total volume flow, wherein the constant total volume flow results from the addition of the volume flow of the dilution air and the volume flow of the exhaust gas, wherein - a tunnel which has fluid passing through it, the tunnel being a dilution tunnel, - a gas conveying means for generating a fluid flow in the tunnel, - an exhaust gas inlet for supplying exhaust gas, and - a venturi nozzle which is used with critical flow, for setting a constant total volume flow, wherein the constant total volume flow results from the addition of the volume flow of the dilution air and the volume flow of the exhaust gas, wherein a measuring point, for determining the volumetric flow rate of the dilution air which is supplied, is provided upstream of the exhaust gas inlet, and a determining means is provided, which is adapted to determine the exhaust gas quantity supplied from the constant total volume which is kept constant by the Venturi nozzle minus the dilution air flow which is supplied and which is determined at the measuring point, wherein the venturi nozzle is arranged upstream of the gas conveying means, and a first flow element is arranged upstream of the venturi nozzle and upstream of the exhaust gas inlet at the measuring point, and wherein the measuring point comprises pressure sensors (P1, P2) for determining the differential pressure upstream and downstream of the first flow element.