Separators used in the oil and gas industry are pressure vessels that segregate well streams into respective liquid and gaseous components. The applications of separators range from on-site primary separation to refinery process separations. Horizontal, vertical, and spherical are the main types of oil and gas separators. Based on the fluids to be separated, the separators can be divided into two groups: oil or gas or water three-phase separator and liquid or gas two-phase separator. Separators can also be classified as degassers, deliquizers, primary-phase, test, low-pressure, and high-pressure separators based on their application. They are usually designed in three stages, namely, preliminary stage, second stage, and third stage to meet the requirements of a project. Gravitational and centrifugal technologies are used to achieve the required efficiency of separation. In addition, the degree of separation is determined based on factors such as separator operating pressure, fluid flow regime (turbulent or laminar), and residence time of the fluid mixture.