Rotating packed beds (RPBs) offer the possibility to intensify mass transfer processes by combining large throughputs with a compact design. To design and dimension RPBs, fundamental knowledge about the hydrodynamics and the operating limits is mandatory. In the present work, the results of experimentally determined upper operating limits for a pilot scale RPB are presented. The upper operating limits were identified visually by the entrainment of liquid towards the gas outlet of the RPB. Gas capacity factors of up to 3.4 Pa-0.5 and liquid loads of up to 51 m(3) M-2 h(-1) were investigated. At these operating conditions a stable operation of the RPB was possible using a full jet nozzle. Changing the nozzle type to flat fan nozzle decreased the upper operating limit significantly. In addition two different packings, a knit mesh and metal foam, were investigated. The influence of the packing materials on the upper operating limit was found to be of minor importance. A comparison of the own experimental data with literature data indicates, that not all of the operating limits reported in the literature may reflect the maximum operating limits that are achievable in RPBs.