Abstract: The separator includes a vertical cylindrical pressure vessel having elliptical top and bottom heads. A mechanical device, referred to as a vortex tube cluster of vertical tubes, is mounted in the upper section of the vessel chamber, spaced above the bottom head to define a lower chamber section for fluid and solids separation. Pressurized drilling fluid returns are directed tangentially into the vortex tubes and a subsequent centrifugal action is generated. Contained gas separates and forms a gas vortex which exits upwardly from the vortex tubes and vessel top. The liquids and solids discharge into the vessel lower chamber section where solids settle by gravity to the bottom. The solids are withdrawn from the base of the vessel by a slurry pump. The oil and water components of the fluid layer also separate by gravity and are individually removed from the vessel.