Abstract The gas liquid cyclone separator is a device that works as a result of the centrifugal force acting on the denser phase of a two-phase flow. This causes the liquid phase which is denser than the gas, to move outward to the cyclone wall. The separated gas comes out by the top, the crude/water blend comes out by the bottom as a two phase stream. The separation time is almost instantaneous and due to its simple design, no moving parts and low cost, the cyclone separators have become an attractive solution for the new oil an gas field developments. The liquid viscosity has a predominant influence in the performance of this kind of separators. As the liquid viscosity increases the shear stresses increase too producing a higher dissipation of the vortex intensity and as a consequence the separation efficiency is diminished. Therefore, the cyclone operational envelope for heavy oils is reduced as compared to light oils. This paper presents the status of the gas-liquid cyclones separation studies related to their performance when used with high viscosity liquids. Experimental and computational studies from different sources, including PDVSA Intevep, are presented for different types of cyclones, with liquid viscosity between 1 and 1500 cP.