Multiphase separators are one of the most prevalent unit operations in any chemical process. They are generally the first process equipment in an oil production platform, and their efficiency influences the performance of all downstream equipment, such as heaters, compressors, and distillation columns. Thus, oilfield separators play a key role in the production capacity of entire facility. In this book, a realistic simulation approach based on Computational Fluid Dynamics (CFD) is developed to provide high-quality visualization of the multiphase separation process. Furthermore, classic separator design methodologies are evaluated and improved design criteria are proposed. A useful method is presented for estimation of the droplet sizes used to calculate realistic separation velocities for various oilfield conditions. The velocity constraints associated with re-entrainment phenomenon are also discussed and novel correlations are provided. This book, also demonstrates the benefits that CFD analyses provide in optimizing the design of new separators and solving problems with existing designs.