A homogeneous catalysis is defined by when a catalyst and its reactant exist in the same phase. A reaction is determined to be a homogeneous catalysis when there is no identifiable boundary between the catalyst and reactant.
Homogeneous catalysis occur most often in liquid and gas phases. However, there are exceptions, such as water and oil, which do not mix, are considered heterogeneous catalysis. Chemical processes that utilize soluble organometallic compounds as catalysts are considered to be homogeneous catalysis. It has been used in a variety of industrial processes, such as the Wacker and Monsanto processes. Examples of homogeneous catalysis include hydroformylation, hydrogenation and transfer hydrogenation.