An exhaust gas system for combustion engines is provided having at least one exhaust gas duct, in particular an exhaust pipe, and having an exhaust gas treatment device such as an oxidation catalyst, an SCR catalyst or a diesel particulate filter downstream of the exhaust gas duct, wherein, to improve the efficiency of downstream gas treatment devices, at least one secondary flow duct, in particular a secondary flow pipe, is provided in the exhaust gas duct with a cross-section reduced with respect to the exhaust gas duct which imparts coerced guidance of some of the exhaust gas flow differing from the actual exhaust gas flow.