Immersed Boundary Method simulations are used to propose a drag correlation for randomly arranged monodisperse spheres. The solid volume fraction is varied from 0.05 to 0.5 and Reynolds number is varied from 0.01 to 1000. The particles have constant relative velocity to fluid and thus the present results are applicable to high Stokes number gas-solid flows. Average drag force acting on particles in both regular and random arrangements is compared with literature and good agreement is observed. At the end a new drag relation for monodisperse spheres is proposed and the physics behind its development is explained. (C) 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.