The metrics for Process Intensification (PI) for multiphase reactors, typically gas-liquid-solid catalyst, are delineated. A multiphase reaction comprises of several steps in series that include diffusional steps. These diffusional resistances can be a serious burden particularly when catalysts having high activity are used. The concept of PI in multiphase reactors involves elimination of the diffusional resistances in the multi step process. Under these conditions the reactor achieves the intrinsic rate of reaction for the specific catalyst used. Consequently, the maximum possible reactor productivity is obtained. The application of this concept is illustrated through three industrially important examples. It has been shown that application of a Venturi Loop Reactor in place of conventional devices results in significant benefits that fall in the realm of PI.