A downer reactor is being expected to provide narrow residence time behavior, because of the concurrent movement of gas and solids in the direction of gravity. In the literature, many studies have shown that the gas/solids distributor on the top of the downer greatly influences the flow conditions. However, the influence of the distribution process on the residence time behavior is not known. Therefore, the influence of mixing behavior of gas/solids flows in the entrance section of a downer reactor on the residence time distribution of the gas phase has been studied experimentally. The investigations show that the solids feeding process and geometry of the entrance region crucially influence the gas residence time distribution and can lead to a broad residence time distribution of the gas. However, for certain geometries and different operating conditions, the entire downer plant can be regarded as similar to a plug-flow system.