Abstract: A gun barrel tank for treating raw crude oil mixtures. The fluid mixture enters through a degassing boot where gas is separated from the liquid. The liquid travels through a central column to a horizontal hydraulic distributor located in the lower area of the tank, first entering a central distributor trough, then passing into open bottom horizontal inverted lateral troughs and finally out through a plurality of metering orifices provided near the top edges of the lateral troughs to provide uniform distribution of the liquid in the tank. A circular oil collection trough provided at the top of the tank has a plurality of V-shaped notches on its top edge over which oil flows into an oil collection trough to provided uniform collection of the separated crude. A circular water collector in the bottom of the tank removes separated water, and solids are removed from the bottom of the tank.