The motion of multiple microcarriers in the liquid cell culture medium of a NASA designed Slow Turning Lateral Vessel (STLV) has been numerically investigated. The associated mass transfer has been studied using a ‘sink-model’. A finite element method is employed to directly simulate the motion of a number of solid microcarrier particles. The motion of the combined fluid-particle system is simulated by using a procedure in which the positions of the microcarriers and of the unstructured mesh grids are updated explicitly, while the velocity and pressure of the fluid and the velocity of the microcarriers are determined implicitly. The migration of the particles is affected by the interaction between them and with the walls. The hydrodynamic forces on the microcarrier particles are also evaluated. The mass transfer is treated as a post-processing procedure by solving the binary mass transfer equation. We provide results for the oxygen mass fraction distribution as a function of time taking into account its consumption by the cells grown on the microcarriers.