Spontaneous oil percolation in French fries was studied dynamically at cellular scale using deep-UV synchrotron radiation enabling to image simultaneously the fluorescence of cell walls and of dyed oil. Experimental results report 75 oil filling kinetics of potato parenchyma cells previously emptied and equilibrated with superheated steam in conditions mimicking immersion frying. Counter-current oil-air flow was found the dominant factor controlling the kinetic of oil penetration, whereas, trapped bubbles delay the passage of oil from the first to the second cell layer for additional several minutes. The frequency of occurrence of passages between layers was assessed much lower than the percolation threshold suggested by the hierarchical honeycomb arrangement of cells. A description relating microscopic oil-air flow and oil uptake is detailed in a companion paper. (C) 2015 American Institute of Chemical Engineers