Disclosed is a compact liquid-liquid separation device useful for the separation of oil and water in hydrocarbon production operations, as well as systems and methods for use thereof. The device includes a separator body of generally vertical pipe having an upper portion and a lower portion, and an inlet to the separator body of generally horizontal pipe in fluid communication with the separator body and attached to the separator body between the upper section and the lower section. The inlet has a round cross-section portion and a reducing area nozzle portion in which the horizontal width of the inlet decreases symmetrically with proximity to the separator body. The vertical interface between the inlet and the separator body has a generally rectangular cross-section.