Gas holdup of water/nitrogen, water-phenol/nitrogen and water-phenol/air systems was successfully measured by a method based on the use of a differential pressure sensor installed on a bubble column reactor, in a wide domain of temperature (from 100 to 300 degrees C) and pressure (from 10 to 30 MPa). These experimental conditions are little or no explored in literature. Results show a predominant influence of the superficial gas velocity, the evaporation of the liquid phase, the ratio of the gas volume flowrate on the liquid volume flowrate and the phenol concentration. Pressure and chemical reaction have little effect on gas holdup. The temperature has an effect in the case of phenol solutions. The different correlations and parameters influence determined in this work are very helpful for the design of gas liquid contactors (for instance bubble column) at high pressure and high temperature.