This paper presented a series of three-dimensional numerical simulations on the thermocapillary-buoyancy flow with Soret effect in a shallow annular pool which was filled with the n-decane/n-hexane mixture with an initial mass fraction of 50%. The Prandtl number and the Lewis number of this binary mixture were 9.08 and 27.89, respectively. The annular pool was heated at the outer cylinder and cooled at the inner cylinder. An adiabatic solid bottom and free surface were considered. The results indicated that the solute concentration gradient depends strongly on the temperature gradient. Due to the Soret effect in the n-decane/n-hexane mixture, the n-decane with a higher density component gathers at the colder area near the inner cylinder. The critical thermal capillary Reynolds number for the incipience of the three-dimensional oscillatory flow in the n-decane/n-hexane mixture is smaller than that in the n-hexane fluid, and decreases with the increase of the aspect ratio. A solute concentration fluctuation which is similar to the temperature fluctuation is observed when the three-dimensional oscillatory flow happens. The nondimensional fundamental oscillation frequency is related to the aspect ratio and the thermal capillary Reynolds number. Meanwhile, the azimuthal wave number decreases with the increase of the aspect ratio, but it is independent of the thermal capillary Reynolds number. (C) 2015 Elsevier Ltd. All rights reserved.