An oxidation furnace for the oxidative treatment of fibers having a housing which is gas-tight, apart from passage areas for the fibers, and a process chamber located in the interior of the housing. A hot working atmosphere can be generated by an atmosphere-generating device, can be blown into the process chamber and flows through the process chamber in processing conditions in a main direction of flow. Deflecting rollers guide the fibers through the process chamber in a serpentine manner in such a way that the fibers lie next to one another as a fiber carpet (22a), wherein the fiber carpet spans a plane between opposite deflecting rollers. A flow measuring system is provided, by means of which a flow profile of the working atmosphere in processing conditions can be generated, and which comprises at least one sensor system for determining the speed of flow, the sensor system being arranged in a sensor region between two adjacent fiber carpets.