The numerical solution of the special integral form of two-dimensional continuity and unsteady Navier Stokes equations is used to investigate vortex states of a horizontal cylinder undergoing forced oscillations in free surface water wave. This study aims to examine the consequence of degree of submergence of the cylinder beneath free surface at Froude number 0.4. Calculations are carried out for a single set of oscillation parameters at a Reynolds number of R = 200. Two new locked-on states of vortex formation are observed in the near wake region. The emphasis is on the transition between these states, which is characterized in terms of the lift force on the cylinder and the instantaneous patterns of vortex structures and pressure contours in the near wake. (C) 2013 Elsevier Ltd. All rights reserved.