In this paper, the so-called monolith loop reactor is introduced. In this reactor, liquid is circulated over a monolith catalyst using a pump while gas-phase circulation is obtained by the pressure difference across the reactor. A model is derived to calculate the liquid hold-up inside the monolith as a function of the liquid circulation flow rate. Gas-liquid mass-transfer measurements in a monolith are compared to a model for capillaries. A combination of the hydrodynamic and the mass transfer models leads to predicted k(L)a values as a function of the power input. The performance of the monolith loop reactor is compared to bubble columns and stirred-tank reactors.