With many of today�s oil wells located offshore, the production of high volumes of water compared to oil poses major challenges to oil operators. The use of liquid�liquid hydrocyclone (LLHC) is one effective way to arrest these uphill problems of produced water. However, the nature of fluid flow within the LLHC device is very vital to the separation process and performance. This study through numerical simulation lends understanding to the way oil�water fluid migrates within LLHC device and shows how the flow structure can affect the efficiency of the separation process. Unsteady wavering flow was realized for the use of the single inlet due to flow imbalance just after entry into the cyclone. This affected the efficiency of separation as water droplets in the vicinity of the reverse flow core boundary could be carried to the overflow. In addition, there was the realization of frequent recirculation zones which cause some fluid droplets to be unseparated. Uniform unwavering fluid flow structure was observed in the case of dual inlet LLHC which assisted in the segregation of the oil and water into their respective core regions as oil-rich core (inner) and water-rich core (outer). The separation efficiency achieved from the use of the dual inlet LLHC outperformed that from the single inlet LLHC. An efficiency of 82.3 was obtained for the dual inlet LLHC as against 73.7 for the single inlet LLHC at 0.5 m3/h. At 1.0 m3/h, a great separation performance of 93.6 was achieved from the dual inlet LLHC, whereas separation efficiency of 88.5 was obtained when the same feed was treated in the single inlet LLHC. © 2019, The Author(s).