The direct coal liquefaction pilot plant at Kashima, Japan, based on the NEDOL Process, was equipped with three bubble column reactors, each of which was 1 m in diameter and 11.8 m in length, connected in series. In order to investigate the hydrodynamic behavior of liquid in the reactors, a gadolinium. tracer was injected to the inlet of the first or third reactor, and the concentration of the tracer was measured at the outlet Of the reactor by a neutron absorption tracer technique. Residence time distribution curves were thus obtained under liquefaction conditions. A pseudo-three-dimensional two-phase fluid dynamic model was developed based on a mixed Eulerian-Lagrangian representation with the Kato-Launder k-epsilon model for turbulent stresses in the reactors. A dynamic simulation was then carried out using a finite-volume solution algorithm. The physical properties of gas and liquid in the reactor were estimated, taking into consideration the evaporation of oil to the gas phase. The model adequately described the measured residence time distribution curves.