This practical guide is designed to help engineers and operators develop a "feel" for selection, specification, operating parameters, and trouble-shooting separators; form an understanding of the uncertainties and assumptions inherent in operating the equipment. The goal is to help familiarize operators with the knowledge and tools required to understand design flaws and solve everyday operational problems for types of separators. The most important gas/liquid separations that take place in oil field operation have been investigated. An inventory has been made of the conditions under which the separations have to take place and which requirements have to be fulfilled. The presently available separator types have been evaluated with respect to the suitability to fulfil the requirements listed above. It appeared that many separator types were not specifically designed for high pressure gas/liquid separation (rather for either atmospheric gas/liquid or high pressure gas/dust separation). It also appeared that in many cases the behaviour of the separator could not be reliably predicted under the conditions of the practical application.