The multiphase separators are generally the first and largest process equipment in an oil production platform. This primary separation step is a key element in the oil and gas production facilities in that downstream equipment, such as compressors, are completely dependent on the efficient performance of these multiphase separators. The literature on this critical unit operation, multiphase separators, abounds with macro studies and design methodologies for two- and three-phase vertical and horizontal separators. There are very few studies that provide the micro details of the actual separation process. In fact, the popular classic methods for separator design, mostly due to a lack of a usable mathematical model for estimation of droplet separation velocities, do result in a conservative design and would specify extremely oversized separators. In order to reflect the current situation and address recent findings, this study will review the important literature on design and CFD simulation of multiphase separators. This review will show the benefits that CFD analyses can provide in optimising the design of new separators and solving problems with existing designs. (c) 2011 Canadian Society for Chemical Engineering