To separate oil and gas from one another, the producer usually employs a separator. Most separators are vertical or horizontal, although a spherical (ball-shaped) design is available. All provide an enclosed space into which the operator pipes produced fluids. Given a chance to remain stationary for a short period, the force of gravity makes the fluids separate. Some are two-phase separators, which means that only oil and gas or emulsion and gas separate inside them. Others are three-phase separators, which means that oil (or emulsion), gas, and water separate inside them. If only relatively small amounts of free water are in the produced fluids, or if some free water remains after the fluids pass through a free-water knockout, then the producer may use a three-phase separator.
As separation occurs inside the separator, the gas goes to the top of the vessel. The operator pipes it to additional gas-handling facilities on the platform—to a glycol dehydrator, for example. If water separates out, operators remove it from the bottom and dispose of it. They remove oil from the middle (or bottom, if they are using a two-phase separator) and transport it to shore if the oil does not require further treatment. Usually, however, water is emulsified in the oil, so the operator pipes this emulsion to treaters elsewhere on the platform. After the treaters break out most of the emulsified water, the operator transports the treated oil to shore.