Experimental and numerical investigations were conducted to study the effect of unsteady mass transfer on the dynamics of an organic droplet released in quiescent water. The situation is important and relevant to deep sea oil spill scenario. The droplet contains two components, one is heavier (immiscible) than water and other is lighter (miscible). When released, with an initial mixture density (890-975 kg/m(3)) lower than that of surrounding water, droplet rises in the column. The mass transfer of lighter solute component into water causes the droplet density to increase and droplet sinks when the density exceeds that of water. A mass-transfer correlation accounting for the loss of the solute, based on Reynolds, Grashoff, and Schmidt numbers was developed. A two-dimensional axisymmetric Computational Fluid Dynamics (CFD) model accounting for species transport was developed to emulate the experimental observations. The study also helped in identifying dominant mass-transfer mechanisms during different stages of droplet motion. (c) 2014 American Institute of Chemical Engineers AIChE J, 61: 342-354, 2015