Gas-liquid-liquid flows are industrially important especially in gas and oil processing. Such flows are inherently unstable and chaotic. Classification and detection of flow patterns is the first step in developing applicable working relation between the flow system parameters - pressure drop, holdup fractions, and phase properties. The book discusses the different flow patterns encountered in gas-liquid-liquid flow through a vertical pipe. Objective identification of the flow patterns based on random signals from an optical probe and their statistical analysis is presented. It also covers analysis of the hydrodynamic parameters - pressure drop and hold up of three phase upflow