A simple model, based on the theory of liquid emulsions, is proposed to develop correlations suitable for estimating gas-liquid interfacial areas for the bubble flow regime in three-phase fixed bed reactors operated with gas and liquid flowing cocurrently upflow. The model is also employed for trickle-bed reactors for estimating the increase in gas-liquid interfacial areas when these reactors are operated under high pressure conditions. It is found that developed correlations account satisfactorily for most of the data of gas-liquid interfacial areas available in the literature for cocurrent upflow three-phase fixed bed reactors and for trickle-bed reactors operated at high pressure conditions.