This article reviews the design features and operating principles of Heater-Treater separators used for the treatment of produced oil with high water content and stable emulsions. The differences from conventional gravity separators are analyzed, including the presence of internal heating elements that enhance separation efficiency and reduce retention time. Key technical requirements for operation and automation are described. It is shown that Heater-Treater ensures improved oil quality with water content below 0.5%, increasing the reliability and cost-effectiveness of treatment processes. The review results confirm the significance of this equipment type for modern oil production and processing conditions.