The hydrodynamics of an inclined rotating tubular fixed bed reactor operated with gas-liquid co-current downflow are studied. Reactor inclination is applied to force phase segregation, while the superimposed rotation of the reactor results in a wetting intermittency via periodic catalyst immersion. The fixed bed is clamped to avoid abrasion of the catalyst. The inclined rotating reactor is presented as a new reactor concept for process intensification of heterogeneous catalytic reactions requiring enhanced mass transfer of the gaseous phase and partial catalyst wetting. Four different flow regimes with stratified, sickle, annular and dispersed flow patterns are determined experimentally by applying a compact gamma-ray computed tomography system. The effects of (i) gas and liquid superficial velocities, (ii) inclination angle and rotational velocity of the reactor and (iii) physico-chemical properties of the liquid phase on the occurrence of the flow regimes are investigated. The results of these investigations are illustrated with flow maps. In addition, pressure drop and liquid saturation depending on the operating conditions are shown.