The mass transfer from two spheres in tandem to an incompressible fluid flow accompanied by chemical reactions (first-order and second-order irreversible) into the fluid was analysed numerically. Creeping flow was assumed. The spheres have the same diameter, initial concentrations and physical properties. The concentration of the transferring species inside the spheres is considered: (1) constant and (2) spatially uniform and varying in time. The mathematical model equations were solved numerically in bispherical coordinates system. The computations focused on the conditions when the interaction between spheres does not influence the mass transfer rate. (C) 2018 Elsevier Ltd. All rights reserved.