Phase-resolved PIV measurements were carried out to provide a thorough characterization of the flow and mixing dynamics occurring in a cylindrical shaken bioreactor when operating conditions such as medium height h, shaking rotational speed N, orbital shaking diameter d(o), and cylinder inner diameter d(i), are varied. A scaling law based on the aspect ratio h/d(i), on the orbital to cylinder diameter ratio d(o)/d(i), and on the Froude number Fr = 2(pi N)(2) d(o)/g, is derived to predict the incipience of flow transition occurring when the free surface orientation starts to exhibit a phase delay to the shaker table position along its orbit; depending on the combination of Fr, d(o)/d(i) and h/d(i) the transport phenomena in the bioreactor are controlled by a horizontal toroidal vortex, or by a vertical one precessing around the cylinder axis. The free surface interfacial area was directly measured by image analysis to assess oxygen transfer potential and compared to an analytical solution valid for low Fr. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 334-344, 2013