Olive stone residues (23%wt) were liquefied in phenol (71%wt) in the presence of sulfuric acid (6%wt) as catalyst at 170degreesC during 2 h. A 500 ml classic reactor under atmospheric conditions was used to establish the characteristics of the new 2001 liquefaction reactor. The liquefied products can be used as raw material for phenol-formaldehyde resins. The batch feeding procedure, the average temperature and the configuration of the reactor largely determined the viscosity and the molecular weight of the liquefied products. These parameters were positively modified by the constantly presence of olive stone moisture and water from depolymerization in the reaction medium. A jacketed cooling wall in the upper half of the 2001 reactor and a heat exchanger were necessary to accelerate vapour condensation, and to improve the contact in the reaction mixture. The recovery of liquefied products was also improved by using a closed container with a pressure-equalizing system that avoids the release of phenol vapour to the atmosphere.