In this work, we focus on two-dimensional, incompressible viscous channel flow over an infinitely long cylinder and examine the effect of controlled rotational cylinder oscillation in reducing the drag exerted on the cylinder. Based on an analysis of the open-loop simulations, a control system is designed that automatically determines the frequency of cylinder oscillation, based on the Reynolds number, to consistently reduce the drag exerted on the cylinder for Reynolds numbers in the range 100-500. (c) 2004 Elsevier Ltd. All rights reserved.