Different points along hydrophobic surfaces like air bubble interfaces in water when probed by atomic force microscope tips reveal distinct behaviors. At some points along the interface the tip suffers a strong attraction within a range of similar to250 nm away from the interface plane; at other points the interface exerts a medium range repulsive force growing stepwise as the tip approaches the interface plane; consequently, the hydrophobic force is a strong function of position. To explain these results, we propose that the water interface structure is formed by a network of nanosized hydrogen-bond connected cages of water molecules of different sizes. (C) 2004 Elsevier B.V. All rights reserved.