The motion of a Newtonian deformed drop freely rising through shear-thinning fluids characterized by the Carreau-Yasuda model was considered experimentally and cornputationally. By numerically evaluating the local viscosity profiles as functions of the shear-rate and the drop shape, it is clear that a numerical approach can be very useful for understanding droplet rise velocities in shear-thinning fluid systems. It was shown numerically that the state and characteristics of the local changes in viscosity around the drop depend significantly on the drop shape. A distinguishing feature of the deformed drop is the formation of a much higher viscosity area at the rear of a drop as a result of the effect of the stagnant flow field behind the drop. Also, the rise velocity of the drop based on the modified Reynolds (Rem) and Morton (M-M) numbers and the representative (effective) viscosity (C eta(0)) was quantitatively evaluated. The variations in these values of Re-M, M-M and C eta(0) were then used to assess the drop rise motion in shear-thinning fluid systems from a practical viewpoint. (c) 2005 Elsevier B.V. All rights reserved.