Optical micro-manipulation has seen a resurgence of interest in recent years which has been due in part to new application areas and the use of tailored forms of light beam. In this paper, experimental observations of fluctuation-driven transport of silica microspheres within a two-dimensional optical potential of circular symmetry are observed. The potential is created by a Bessel light beam. The optical field is tailored to break the symmetry and create a static tilted periodic (washboard) potential. Transitions between locked and running modes may be observed. The running mode manifests itself by rapid accumulation of particles at the beam centre. We discuss what happens with mixtures of particles in such an optical potential.