The present work addresses the numerical simulation of rising droplets with clean interface. An interface tracking methodology was applied to simulate the particular behavior of water-immersed toluene drops. The obtained transient velocity profiles were compared with experimental data, confirming the methodology's capability to represent this two-phase flow. Numerical simulations enable scrutinizing many flow details which are not accessible experimentally. In this regard, the elements linked to the velocity oscillatory behavior of droplet sizes between diameters of 2.2 and 3 mm are discussed. It could be verified that velocity oscillations were directly related to variations in shape, internal circulation and flow separation. Simulations indicated that three-dimensional shape asymmetries are associated with vorticity accumulation in preferential regions of the drop, which disturb the internal circulation pattern. In the oscillatory size range, flow separation causes periodic vortex detachment, enabling formation of a double-thread wake. Evaluation of non-dimensional parameters further disclosed the relation of the transitory behavior and steady state drop shape. (C) 2018 Elsevier Ltd. All rights reserved.