The coalescence phenomenon is of capital importance in the design and performance of multiphase contactors. Although studied for several decades, it is still not completely understood. The present project aims to improve our knowledge on the subject in the following way: to determine experimentally a relation between coalescence efficiency and the crucial control parameters (bubble properties, liquid properties, liquid flow condition). Bubble coalescence will be studied experimentally in a laboratory cell under well-defined conditions. Then, these small scale data will be related to the coalescence in real gas-liquid dispersions in bubble column reactors.