A vessel that separates the well fluids into gas and two types of liquids: oil and water. A three-phase separator can be horizontal, vertical or spherical. This type of separator is commonly called a free-water knockout separator because its main use is to remove any free water that can cause problems such as corrosion and formation of hydrates or tight emulsions, which are difficult to break.

The liquids (oil, water) leave the vessel at the bottom through different valves, and the gas leaves the vessel at the top, passing through a mist extractor to remove the small liquid droplets in the gas.